An optical scanning apparatus includes a light source which emits an optical beam, a deflection scanning unit, and a control unit. The deflection scanning unit includes a rotating polygonal mirror which deflection-scans the optical beam emitted from the light source so that the optical beam will scan an object to be scanned, and a drive unit which rotationally drives the rotating polygonal mirror. The control unit controls the rotational speed of the rotating polygonal mirror by accelerating or decelerating the drive unit at a predetermined time during one rotation of the rotating polygonal mirror. The predetermined time is a time when a deviation in length of a scanning line formed by each reflecting surface of the rotating polygonal mirror becomes relatively small.