A multi-beam optical scanner includes shaping optics (42) by which a plurality of light beams issued from light emitting portions (411, 412) are shaped to be substantially parallel in a primary scanning direction, a deflector having reflecting faces (45) that reflect and deflect the plurality of light beams and scanning optics (46) by which the plurality of light beams reflected and deflected by the reflecting faces (45) are scanned across a plane (48) to be scanned as a plurality of adjacent beam spots, wherein the distance from the rear principal plane of the shaping optics (42) to the front principal plane of the scanning optics 46 is expressed by f1+f2, where f1 and f2 are the focal lengths of the shaping optics (42) and the scanning optics (46), respectively, in the primary scanning direction.