An image forming apparatus includes an optical sensor configured to detect reflected light from a detection image formed on the transfer member. The optical sensor includes a light emitting element configured to emit light for irradiating the detection image at a predetermined angle of incidence, a first light receiving element arranged at a position at which diffused reflected light from the detection image is received at a first angle of reflection, and a second light receiving element arranged at a position at which the diffused reflected light from the detection image is received at a second angle of reflection.