A developing device of developing a latent image formed on an image bearer includes a developing roller, a developer regulator of a round-bar shape, and a holder. The developing roller carries developer. The developer regulator faces the developing roller to regulate an amount of the developer carried on a surface of the developing roller. The holder has a first hole, a second hole, and a projection. An end of the developer regulator is inserted in the first hole. A shaft at an end of the developing roller is inserted in the second hole. The projection protrudes toward an inside of the at least one of the first hole or the second hole and holds the end of the developer regulator and the shaft.

An image forming apparatus includes an image carrying member, a charging device, an exposure device, a development device, and a development voltage power supply. The image carrying member has an amorphous silicon photosensitive layer formed on its surface. The development device includes a developer carrying member carrying two-component developer containing toner and carrier. The development voltage power supply applies to the developer carrying member a development voltage having an alternating-current voltage superposed on a direct-current voltage. When the blank part potential on the image carrying member is V0 [V], the direct-current voltage is Vdc [V], the peak-to-peak value of the alternating-current voltage Vac is Vpp [kV], and the gap between the image carrying member and the developer carrying member is Ds [mm], 10V0Vdc90 and 1.2Vpp/Ds3.5 are fulfilled.

An image forming apparatus according to the present disclosure includes: an image forming portion configured to apply a bias voltage between a first carrier with a surface to be charged and a second carrier configured to hold toner to be adhered to the first carrier to move the toner from the second carrier to a developing area of the first carrier to develop the developing area of the first carrier; a current detection portion configured to detect a target current that flows between the first carrier and the second carrier during development; a temperature detection portion configured to detect a temperature inside the apparatus; and a cooling control portion configured to execute a predetermined cooling operation based on a detected current that is detected by the current detection portion and a detected temperature that is detected by the temperature detection portion.

A developing device includes a second rotatable member and a guiding portion having an inclined surface. In a case where a normal component of magnetic flux density of the second rotatable member is Br, a tangential component of the magnetic flux density is B, an absolute value of a synthetic component of Br and B is |B|=(Br.sup.2+B.sup.2), and a distance from an arbitrary point to the inclined surface is d, a maximum position which is a position where |B|/d as an index obtained by dividing |B| by d becomes maximum is positioned on a side downstream, with respect to a rotational direction of the second rotatable member, of a closest position on the outer peripheral surface of the second rotatable member, which is a position where the outer peripheral surface of the second rotatable member is closest to the guiding portion.

A developing device includes a first rotatable member, a second rotatable member, a first feeding screw, a second feeding screw, and a guiding portion. In a case where a normal component of magnetic flux density of the second rotatable member is Br, a tangential component of the magnetic flux density is B, and an angle of a magnetic brush is arctan (Br/B), there is a portion where the angle of the magnetic brush is 45 or more in a range from an intersection point where a rectilinear line passing through an end portion of the guiding portion and a rotation center of the second rotatable member crosses an outer peripheral surface of the second rotatable member, to a closest point where the outer peripheral surface of the second rotatable member is closest to the guiding portion.

A magnet member is non-rotatably secured inside a developing sleeve, and includes a plurality of magnetic poles arranged along a rotation direction of the developing sleeve. The magnetic poles include a main pole facing the image carrying member, and a peeling pole that is disposed downstream of and adjacent to the main pole in the rotation direction of the developing sleeve and that peels off the developer carried on the developer carrying member. A magnetic-flux-density peak-position of the main pole is located below a horizontal line passing through a rotation center of the developing sleeve, and as viewed from an axial direction, an angle that a line extending from the magnetic-flux-density peak-position of the main pole to the rotation center of the developing sleeve forms with respect to the horizontal line passing through the rotation center of the developing sleeve is 40 or larger but 80 or smaller.

In the first potential difference adjustment mode, the fogging toner amount is predicted from a toner charge amount and a fogging toner current sensed by a current sensing portion with a zero surface potential on the image carrying member. In the second potential difference adjustment mode, the carrier development amount is predicted from a toner concentration, a carrier charge amount calculated based on the toner charge amount, and a carrier development current sensed by the current sensing portion with a zero surface potential on the image carrying member.