An image forming apparatus includes: a receiving unit configured to receive reflection light emitted by a light emitting unit, and output a detection signal corresponding to an amount of received reflection light; a detection unit configured to output, as an output signal, a signal corresponding to a difference between a value that corresponds to an amount of reflection light from a first position at which a detection image having one or more lines in a direction different from a movement direction is formed and a value that corresponds to an amount of reflection light from a second position different from the first position; and a control unit configured to control an image formation condition related to density of an image to be formed, based on a peak value of the output signal.