An image forming apparatus includes an image bearing member; a plurality of chargers for injection charging of the image bearing member; a latent image forming device, disposed downstream of the plurality of charging members with respect to a moving direction of a peripheral surface of the image bearing member, for forming a latent image on the image bearing member having been charged by the plurality of charging members; a potential detecting device for detecting a surface potential of the image bearing member after passing by the plurality of charging members, wherein the plurality of chargers include a first charger and a second charger disposed at a most downstream position with respect to the moving direction, and wherein the image forming apparatus is operable in a control mode in which a bias voltage applied to the first charger is changed with a bias voltage applied to the second charger unchanged.