A lens for optical scanning condenses luminous flux deflected by an optical deflector
to a plane to be scanned in a scanning image forming optical system. The lens is
made of a plastic material by molding. A reference axis of an N-th order approximating
curve of refractive index distribution n(x) of the lens is away from a center
of a passing area, through which the luminous flux passes in the lens, by equal
to or more than 10% of the width of the passing area.
