Image forming apparatus capable of suppressing occurrence of image defects in response to difference in carrier resistance and obtaining high image quality

An image forming apparatus comprising:

• an image carrier having a photosensitive layer and being formed an electrostatic latent image on a surface thereof;
• a charging unit that charges the surface of the image carrier;
• a developing unit having a developer carrier that carries toner in a two-component developer that includes a toner and a magnetic carrier on a surface thereof, and forms a toner image by adhering the toner to the electrostatic latent image that is formed on the image carrier;
• a developing power supply that applies a developing voltage obtained by superimposing an AC voltage on a DC voltage to the developer carrier;
• a current detecting unit that detects the developing current that flows between the developer carrier and the image carrier when the developing voltage is applied to the developer carrier;
• and
• a control unit that controls the operation of the image carrier, the charging unit, the developing unit, and the developing power supply;
• wherein
• the control unit causes the charging unit to charge the surface of the image carrier, and when the developing voltage is applied to the developer carrier by the developing power supply, derives the carrier resistance based on the developing current detected by the current detecting unit, and controls an AC amplitude of the AC voltage based on the carrier resistance.