To realize a low-cost optical scanner reducing a beam spot diameter by considering even temperature variation and also securing beam spot positional accuracy with high precision.

The optical scanner is equipped with: a light source 11; a deflector 14 for deflecting light beams 21 from the light source; a coupling lens 12 for coupling the light beams from the light source; a first optical system for guiding the light beams from the coupling lens to the deflector 14; a scanning optical system 15 for guiding the light beams deflected by the deflector on a surface 16 to be scanned; and liquid crystal elements 43 which are arranged in the optical path from the light source to the surface to be scanned and which is phase modulated and driven by an electric signal. The first optical system is characterized in that it is composed of lenses 13, 22 having at least [1] a positive power face in the sub scanning direction and [2] a positive power face in the main scanning direction.