An optical scanner according to the present invention comprises a first imaging optical system consisting of a collimator lens and a cylindrical lens, a light deflector reflecting/deflecting a light beam for scanning, and a second imaging optical system consisting of an f-&thgr; lens and an anamorphic lens. The f-&thgr; lens has three groups of lenses, i.e., a first lens having negative refracting power, a second lens having positive refracting power and a third lens having positive refracting power. The f-&thgr; lens is formed to satisfy relational expressions L/f