An image forming apparatus 100 includes: a common voltage-applying unit 8 that applies a voltage to charging-assistant members 7Y, 7M, and 7C of a plurality of image forming portions PY, PM, and PC; and a control unit 110, at the start of applying a voltage to the charging-assistant members of the plurality of image forming portions by the voltage-applying unit 8, switches the absolute value of the applied voltage from a smaller first value to a larger second value when images are formed by the plurality of image forming portions.