1. An image forming apparatus comprising: a photosensitive member; a charging unit configured to charge the photosensitive member; a light source configured to emit a light beam for exposing the charged photosensitive member, wherein the light source includes a plurality of light emitting elements; a current supply unit configured to supply a drive current to the light source to cause the light source to emit the light beam, wherein the drive current includes a bias current; a light receiving unit configured to receive a light beam emitted by any one of the light emitting elements to which the drive current is supplied and a light beam emitted by a light emitting element, to which the bias current is supplied, other than the any one of the light emitting elements; a potential detection unit configured to detect a potential of the photosensitive member; and a control unit configured to control a value of the bias current, wherein the control unit controls the light source such that a plurality of the electrostatic latent pattern images, of which a potential is different to each other and is different to a charging potential of the photosensitive member charged by the charging unit, is formed on the photosensitive member, and the control unit controls the bias current supplied to the any one of the light emitting elements based on an amount of light which the light receiving unit receives and a relationship between the charging potential and the potentials of the plurality of the electrostatic latent pattern images detected by the detection unit.