An optical scanner that performs scanning by deflecting plural light beams using a single deflector. The optical scanner includes plural pre-scanning optical systems configured to emit the plural light beams and each including a light source. A first of the pre-scanning optical systems emits a first of the light beams to be deflected by the deflecting unit. A second of the pre-scanning optical systems emits a second of the light beams and is disposed in the position different from a position of the first pre-scanning optical system in a rotational axis direction of the deflector.