The electrophotographic apparatus includes: an electrophotographic photosensitive member; a charging unit; an image-exposing unit; a charge transfer amount-sensing unit for sensing the amount of charge transferred to the electrophotographic photosensitive member; and an exposed portion potential-controlling unit for controlling the potential of each of the exposed portions of the electrophotographic photosensitive member based on a sensing result, which is obtained by charging the electrophotographic photosensitive member with the charging unit, performing image exposure with the image-exposing unit in at least one light amount weaker than a light amount in which the normalized radius of curvature R of the electrophotographic photosensitive member represented by the following equation (E1), the normalized radius of curvature being obtained by a method of measuring an EV curve, shows a minimum, and in at least two light amounts stronger than the light amount in which the normalized radius of curvature shows the minimum.

[00001]$\begin{array}{cc}R=\frac{{\left[1+{\left(\frac{\mathrm{dy}}{\mathrm{dx}}\right)}^2\right]}^{3/2}}{.Math.\frac{d^2}{{\mathrm{dx}}^2}.Math.}& \left(E1\right)\end{array}$

The electrophotographic apparatus includes: an electrophotographic photosensitive member; a charging unit; an image-exposing unit; a charge transfer amount-sensing unit for sensing the amount of charge transferred to the electrophotographic photosensitive member; and an exposed portion potential-controlling unit for controlling the potential of each of the exposed portions of the electrophotographic photosensitive member based on a sensing result, which is obtained by charging the electrophotographic photosensitive member with the charging unit, performing image exposure with the image-exposing unit in at least one light amount weaker than a light amount in which the normalized radius of curvature R of the electrophotographic photosensitive member represented by the following equation (E1), the normalized radius of curvature being obtained by a method of measuring an EV curve, shows a minimum, and in at least two light amounts stronger than the light amount in which the normalized radius of curvature shows the minimum.

[00001]$\begin{array}{cc}R=\frac{{\left[1+{\left(\frac{\mathrm{dy}}{\mathrm{dx}}\right)}^2\right]}^{3/2}}{.Math.\frac{d^2}{{\mathrm{dx}}^2}.Math.}& \left(E1\right)\end{array}$

Provided is an electrophotographic photosensitive member that includes a support, a charge generation layer on the support, and a charge transfer layer on the charge generation layer and that satisfies specifications on an EV curve based on a measurement method of NESA-EV curve. The electrophotographic photosensitive member can exhibit high character quality and a digital gradation characteristic in a low-line-number halftone while maintaining an analog gradation characteristic in a high-speed process.

Provided is an electrophotographic photosensitive member that includes a support, a charge generation layer on the support, and a charge transfer layer on the charge generation layer and that satisfies specifications on an EV curve based on a measurement method of NESA-EV curve. The electrophotographic photosensitive member can exhibit high character quality and a digital gradation characteristic in a low-line-number halftone while maintaining an analog gradation characteristic in a high-speed process.

An electrophotographic photosensitive member has a charge generation layer having a film thickness of 0.2 μm or larger and a charge transport layer on a support, wherein in a case where, at 23.5° C. and 50% RH, the photosensitive member is subjected to operations and measurement of: specific (1), (2), (3) and (4), an absolute value of a slope α of a linear approximation straight line is 4×10.sup.−3 or smaller, in a range where the electric field strength E is 10 to 40 V/μm, which is expressed by a relational expression between a recombination constant P.sub.e and an electric field strength E, which is obtained from a specific graph which has been obtained by repeatedly performing the specific operations and measurement of (1) to (4) while changing I.sub.exp from 0.000 to 1.000 μJ/cm.sup.2 at intervals of 0.001 μJ/cm.sup.2.

An electrophotographic photosensitive member has a charge generation layer having a film thickness of 0.2 μm or larger and a charge transport layer on a support, wherein in a case where, at 23.5° C. and 50% RH, the photosensitive member is subjected to operations and measurement of: specific (1), (2), (3) and (4), an absolute value of a slope α of a linear approximation straight line is 4×10.sup.−3 or smaller, in a range where the electric field strength E is 10 to 40 V/μm, which is expressed by a relational expression between a recombination constant P.sub.e and an electric field strength E, which is obtained from a specific graph which has been obtained by repeatedly performing the specific operations and measurement of (1) to (4) while changing I.sub.exp from 0.000 to 1.000 μJ/cm.sup.2 at intervals of 0.001 μJ/cm.sup.2.

An electrophotographic photosensitive member includes: a support; an undercoat layer; a charge generation layer; and a charge transport layer, wherein the undercoat layer contains a polyamide resin and a titanium oxide fine particle, and on the surface of the undercoat layer, an arithmetic mean roughness Ra and an average length Rsm of a roughness curve element both according to JIS B0601:2001 satisfy Ra≤50 nm and 0.1≤Ra/Rsm≤0.5; and the charge generation layer contains a hydroxygallium phthalocyanine pigment, wherein the hydroxygallium phthalocyanine pigment includes crystal particles having a crystal form exhibiting peaks at 7.4°±0.3° and 28.2°±0.3° at Bragg angles 2θ in a spectrum of X-ray diffraction using a CuKα, ray; and in a size distribution of the crystal particles, which is measured using small-angle X-ray scattering, a peak exists in a range of 20 to 50 nm, and the peak has a half-value width of 50 nm or smaller.

An electrophotographic photosensitive member includes: a support; an undercoat layer; a charge generation layer; and a charge transport layer, wherein the undercoat layer contains a polyamide resin and a titanium oxide fine particle, and on the surface of the undercoat layer, an arithmetic mean roughness Ra and an average length Rsm of a roughness curve element both according to JIS B0601:2001 satisfy Ra≤50 nm and 0.1≤Ra/Rsm≤0.5; and the charge generation layer contains a hydroxygallium phthalocyanine pigment, wherein the hydroxygallium phthalocyanine pigment includes crystal particles having a crystal form exhibiting peaks at 7.4°±0.3° and 28.2°±0.3° at Bragg angles 2θ in a spectrum of X-ray diffraction using a CuKα, ray; and in a size distribution of the crystal particles, which is measured using small-angle X-ray scattering, a peak exists in a range of 20 to 50 nm, and the peak has a half-value width of 50 nm or smaller.

Provided is an electrophotographic apparatus which uses a light emitting diode array as an exposure unit and exposes a photosensitive member to a quantity of light from the LED array whose average light quantity satisfies 0.8×Emin or more and 1.1×Emin or less on condition that a normalized radius of curvature R of a normalized graph derived from the E-V curve of the photosensitive member has a minimum value of 0.24 or less, and a light quantity at the minimum value of the normalized radius of curvature R is Emin [μJ/cm.sup.2]. This electrophotographic apparatus prevents both the occurrence of image unevenness due to light quantity variation among the elements of the LED array and the generation of ghost images due to a rest potential.

Provided is an electrophotographic apparatus which uses a light emitting diode array as an exposure unit and exposes a photosensitive member to a quantity of light from the LED array whose average light quantity satisfies 0.8×Emin or more and 1.1×Emin or less on condition that a normalized radius of curvature R of a normalized graph derived from the E-V curve of the photosensitive member has a minimum value of 0.24 or less, and a light quantity at the minimum value of the normalized radius of curvature R is Emin [μJ/cm.sup.2]. This electrophotographic apparatus prevents both the occurrence of image unevenness due to light quantity variation among the elements of the LED array and the generation of ghost images due to a rest potential.