To provide an optical scanner capable of attaining compatibility between making a beam spot diameter minute and enlarging the depth of focus without being accompanied by an increase in cost.

An optical scanner includes: a laser diode (light source) 20; a collimator lens 21 for converting a light beam L emitted from the laser diode 20 into parallel light; a cylindrical lens 23 for converting the parallel light from the collimator lens 21 into linear light; a polygon mirror (deflector) 24 for deflecting the linear light from the cylindrical lens 23; and fθ lenses (scanning lens) 25 and 26 for imagining at a uniform speed the linear light deflected by the polygon mirror 24 on photosensitive drums (surface to be scanned) 2a to 2d. An optical attenuation part 21b having an annular shape with an optical axis thereof centered is provided on a light passage range of an incident surface (or an emitting surface) in the collimator lens 21 (or the cylindrical lens 23).