An optical scanning apparatus includes a light source, a deflector that deflects a light beam in a main scanning direction, an incident optical system that makes the light beam enter the deflecting surface in a sub-scanning section, and an imaging optical system that includes at least one imaging optical element and condenses the light beam onto a surface to be scanned, in which 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 such that an origin position line exists in a region sandwiched between marginal rays at two sub-scanning direction ends of the light beam, 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.