An optical scanning apparatus includes a first polarizing member and a second polarizing member between a light source and a MEMS mirror that is a deflection mirror. The first polarizing member reflects a first polarization component included in a beam light emitted from the light source so as to squarely enter the MEMS mirror and passes a second polarization component having a phase difference of a half-wavelength with respect to the first polarization component. The second polarizing member is provided between the first polarizing member and the MEMS mirror to pass the first polarization component reflected by the first polarizing member therethrough twice before and after being reflected by the MEMS mirror to change the first polarization component into the second polarization component. A rotation axis of the MEMS mirror is parallel to an optical axis of the beam light immediately before being reflected by the first polarizing member.