An image forming apparatus includes a photosensitive drum, a developing roller, a cam, a developing motor, a first transmission mechanism, and a second transmission mechanism. The cam moves the developing roller between a contacting position where the developing roller is in contact with the photosensitive drum and a separated position where the developing roller is separated from the photosensitive drum. The developing motor drives both the developing roller and the cam, and is rotatable in a normal rotating direction and a reverse rotating direction. The first transmission mechanism engages power transmission from the developing motor to the developing roller when the developing motor rotates in the normal rotating direction, and disengages the power transmission when the developing motor rotates in the reverse rotating direction. The second transmission mechanism can engage power transmission from the developing motor to the cam, irrespective of the rotating direction of the developing motor.