An image forming apparatus comprises: a sensor that includes a light-emitting part for emitting light to a moving body and a light-receiving part; a light-incidence adjusting mechanism that is able to alternatively select from a first state where the light-incidence adjusting mechanism causes light which have been emitted from the sensor and then reflected by the moving body to enter the sensor and a second state where the light-incidence adjusting mechanism causes a reflected light of light emitted from the sensor not to enter the sensor; and a processing unit that causes the sensor to emit light, and corrects output of the sensor when the light-incidence adjusting mechanism is in the first state on the basis of output of the sensor when the light-incidence adjusting mechanism is in the second state.