A scanning optical system includes a deflector for deflecting a laser
light flux from a light source and a second imaging optical system for
focusing the laser light flux deflected by the deflector on a target
scanning surface. The second imaging optical system has at least one
optical function surface on which an optical function portion including a
plurality of convex portions arranged therein so as to have a serrate
cross section is formed in at least part thereof. The optical function
surface is formed so that a width of each of the convex portions in an
arrangement direction in which the convex portions are arranged is larger
than a width of the laser light flux in the arrangement direction, which
enters the optical function surface.