An optical scanner includes a light source including a plurality of light emitting elements, a polygon mirror which deflects light from the light source for scanning a surface of a subject, an optical element arranged between the light source and the polygon mirror, having optical power in a sub scanning direction, a synchronous detector which detects the light deflected by the polygon mirror for synchronous detection and generates a signal for controlling a timing at which the scanning of the surface is started, and a fixing element which secures one end of the optical element. The light emitting elements of the light source are aligned with a certain tilt angle relative to the sub scanning direction. Light from one of the light emitting elements disposed closest to the fixing element in a main scanning direction is used for synchronous detection.