Optical scanning apparatus and image forming apparatus

An image forming apparatus comprising:

• an optical scanning apparatus including
• a light source,
• a deflector that deflects, by a deflecting surface, a light beam emitted by the light source in a main scanning direction for scanning,
• an incident optical system that makes the light beam emitted by the light source obliquely enter the deflecting surface of the deflector in a sub-scanning section perpendicular to the main scanning direction, and
• an imaging optical system that includes at least one imaging optical element and condenses the light beam deflected by the deflecting surface of the deflector onto a surface to be scanned,
• wherein at least one of an incident surface and an exit surface of the at least one imaging optical element is decentered in the sub-scanning section including an optical axis of the imaging optical system such that an origin position line exists in a region sandwiched between marginal rays at two sub-scanning direction ends of the light beam deflected by the deflecting surface of the deflector, the origin position line being extended in the main scanning direction and passing through an origin of an aspherical surface formula defining a surface shape of each of the incident surface and the exit surface in the sub-scanning section including the optical axis of the imaging optical system;
• a developer that develops, as a toner image, an electrostatic latent image formed on a photosensitive member arranged on the surface to be scanned by the light beam scanned by the optical scanning apparatus;
• a transfer device that transfers the developed toner image to a transfer material;
• and
• a fixer that fixes the transferred toner image to the transfer material.