An image forming apparatus includes image bearing members that bear formed images; a driving source that rotationally drives the image bearing members and whose rotational direction is switchable between a first direction and a second direction; a first driving-force transmitting unit that transmits a rotational driving force of the driving source rotationally driven in the first direction as a unidirectional rotational driving force to the image bearing members; and a second driving-force transmitting unit that transmits a rotational driving force of the driving source rotationally driven in the second direction as a unidirectional rotational driving force to one or more of the image bearing members and does not transmit the rotational driving force to a remaining one or more of the image bearing members. The first and second driving-force transmitting units are switched therebetween by changing the rotational direction of the driving source.