An electrophotographic blade to be brought into contact with a contact member, comprises a plate spring, and a resin layer that covers at least a part of a surface of the plate spring to form a contact region that comes into contact with a contact member. In the state where one of ends of the plate spring is fixed, a length (L) from the fixed end to the another end is 5 mm to 20 mm, and a force needed to displace the another end by 1 mm is 5 N/m to 100 N/m. The resin layer satisfies the requirements: (1) the thickness of the resin layer is 0.05 mm to 2.00 mm, (2) the tan δ value of the resin layer in the range of 5° C. to 40° C. is 0.05 to 0.70, and (3) the elastic modulus of the resin layer is 1.0 to 60.0 MPa.

An example developing device includes a housing to contain a developer and having an opening, a developing sleeve provided in the housing and partially exposed to the outside of the housing through the opening, a magnetic member including a plurality of magnetic poles and located inside the developing sleeve, and an elastic member blocking an inflow of air through a space between a downstream edge of the opening in a rotation direction of the developing sleeve and an outer circumferential surface of the developing sleeve. The elastic member includes a fixed portion fixed to the housing at a position adjacent to the downstream edge of the opening and an extension portion extending from the fixed portion in a bent form in the rotation direction of the developing sleeve to be elastically in contact with the surface of the developing sleeve.

A change of a magnetic flux density distribution adjacent to a regulating blade 9 opposed to a developer regulation pole is suppressed at a low cost, while suppressing influence to design latitude of magnetic poles. A position on the outer peripheral surface of the developing sleeve where the magnetic flux density in the normal line direction of the outer peripheral surface of the developing sleeve is a maximum value position. The position on the outer peripheral surface of the developing sleeve 8 corresponding to a center portion position of the half peak range of the magnetic flux density distribution of the developer regulation pole is called half peak center portion. The developer regulation pole is formed such that the maximum value position is deviated not less than 3° in the circumferential direction of the developing sleeve from the half peak center portion position, and the position when the regulating blade 9 opposite is the developing sleeve is in a side of the maximum value position in which the half peak center portion position exists.

A developing device includes a housing, a developing roller, a developer stirring member, and a layer thickness regulating member. The developing roller includes a stationary magnet and a sleeve. The stationary magnet includes a first magnetic pole having a specific polarity, and a second magnetic pole lying downstream of the first magnetic pole and having the same polarity as the first magnetic pole. In an entire inter-pole region between the first magnetic pole and the second magnetic pole, the stationary magnet produces a magnetic force including a horizontal component that keeps the specific polarity and has a value greater than zero (mT). The inter-pole region includes a flat area where a horizontal magnetic force component having a minimum absolute value exits and the horizontal magnetic force component changes within a range of 0.5 (mT) or less, the flat area extending over a range of 10 degrees or more.

A development device, includes: a developer bearing member; a magnet that is stored in the developer bearing member and has a development pole; and a regulation portion that is disposed to face the developer bearing member for regulating an amount of developer carried on the developer bearing member, wherein the regulation portion is disposed such that, when a magnetic flux density of the development pole in the normal direction with respect to a surface of the developer bearing member is defined as positive, a magnetic flux density becomes positive in the entirety of a region which is upstream of a development region where the developer and an image bearing member are in contact with each other so as to develop an electrostatic latent image formed on the image bearing member and which is downstream of the regulation portion in a rotation direction of the developer bearing member.

A toner circulation and a toner reservoir are formed in the vicinity of a developing roller. A member to form a toner reservoir is movable and is stopped during at least an image-forming period.

A developing blade has a protrusion that protrudes toward a developing roller in an opposing portion facing the developing roller. When the potential difference between a supply bias and a developing bias is denoted by Δ(V), a contact pressure of the developing blade with respect to the developing roller is denoted by X (gf/cm), and a height of the protrusion from the opposing surface that faces the developing roller at a position further toward a tip side than the protrusion is denoted by H (mm) and a length of the opposing surface in the rotation direction of the developing roller is denoted by L (mm), when viewing a cross section perpendicular to the rotation axis of the developing roller, 0.05≦H≦0.1, 0.15≦L≦1.0, and 15≦X≦60 are established, and at least Δ≧−5*X−125 is satisfied.

A regulation member includes an opposed surface and a contact surface in a portion corresponding to an image forming area. The opposed surface is opposed to a developer bearing member. The contact surface protrudes from the opposed surface and has a height different from that of the opposed surface. An end seal seals a gap between a frame body, the developer bearing member, and the regulation member. The regulation member further includes an area not having the contact surface between the image forming area and a sealing area in which the regulation member and the end seal overlap. In the sealing area, a step between the opposed surface and the contact surface has a height of greater than or equal to 0 mm and not greater than 0.10 mm.

A developing blade has a protrusion that protrudes toward a developing roller in an opposing portion facing the developing roller. When a height of the protrusion from an opposing surface that faces the developing roller at a position further toward a tip side than the protrusion is denoted by H (mm) and a length of the opposing surface extending toward the tip side perpendicular to an axial line direction of the developing roller is denoted by L (mm), when viewing a cross section perpendicular to a rotation axis of the developing roller, the following conditions are satisfied:

0.05≦H≦0.3, and

0.15≦L≦1.0.

A development device includes a development housing, a development roller, a supply roller and a layer thickness regulating member. The development housing stores a nonmagnetic one-component toner. The development roller is formed by a cylindrical elastic body, and moves in a same direction as a rotational direction of a rotatable photosensitive drum at a development nip area while coming into contact with the photosensitive drum. The supply roller is formed by a cylindrical elastic body, and supplies the toner to the development roller and collects the toner from the development roller. The development roller has a surface free energy within a range of 5 mJ/m.sup.2 or more and 27 mJ/m.sup.2 or less.