Patent ID: 6958764

Claim:
A scanning optical apparatus comprising: incident optical means for causing at least one light beam emitted from light source means to be incident on deflection means; and image formation means consisting of one refractive optical element and one diffraction optical element for imaging the at least one light beam reflected and deflected by the deflection means on a surface to be scanned, wherein a front focus position of the diffraction optical element in the sub-scanning cross-section is provided between a power arrangement in the sub-scanning cross-section of an on-axis of the refractive optical element and a power arrangement in the sub-scanning cross-section of an off-axis of the refractive optical element, in an optical axis direction; wherein the diffraction optical element is provided between the refractive optical element and the surface to be scanned, in the optical axis direction; and wherein even if a position of said refractive optical element is shifted by 0.1 mm vertically from the optical axis in a sub-scanning cross-section, an on-axis principal ray and an off-axis principal ray of the at least one light beam reach the surface to be scanned at heights whose difference in the sub-scanning direction is less than ±10 μm.