An optical scanning apparatus includes a light source, a light source driving unit that turns on the light source according to image information, a deflector that deflects and scans a light beam emitted from the light source according to sinusoidal vibration, and a scanning/imaging optical system that guides the light beam from the deflector to a scanned surface. The scanning/imaging optical system satisfies two conditions, i.e., (1) provided that the deflector moves in such a manner that an angular velocity is constant, linearity is made larger at a most peripheral image height than at a central image height within a range of an effective writing width, and (2) when a deflection angle of the deflector has a sinusoidal characteristic, the linearity is made smaller at the most peripheral image height than at the central image height within the range of the effective writing width.