PURPOSE: To provide a rotational speed stabilizer for a photosensitive drum, capable of preventing a situation that the photosensitive drum is affected by backlash on a driving torque transmitting element and the constant velocity rotation of the photosensitive drum is disturbed.

CONSTITUTION: In an electrophotograph image forming device providing a photosensitive drum driving mechanism constituted by coaxitally and integrally supporting the shaft center of the photosensitive drum 29 by a photosensitive drum driving gear 33 receiving the transmission of driving force from a driving motor 27 the photosensitive drum driving gear 23 is connected, at least, to another load 28 to be driven, to transmit the driving force. As the load 28 to be driven, a developing device can be used.