A post objective type optical scanner for having a light source for emitting a light beam having a first width in the scanning direction and a second width in the sub-scanning direction, a single lens having an incident surface and an emergent surface and including a scanning optical system having a first light source side principal point, and a sub-scanning optical system having a second light source side principal point, for converting a light beam emitted from the light source having a scanningwise width and a subscanningwise width, the scanning optical system converting the first width of the light beam into the scanningwise of the scanning beam while the sub-scanning optical system converting the second width of the light beam into the subscanningwise width of the scanning beam. The distance of the first light source side principal point from the light source is greater than the distance of the second light source side principal point from the light source. The incident surface of the single lens is toric, having an aberration correction surface for the sub-scanning optical system, while the emergent surface is toric or cylindrical, having an aberration correction surface for the sub-scanning optical system.