An optical scanning apparatus in which keystone distortion non-linearity distortion in a projected image can be excellently corrected is provided. An optical scanning apparatus has light source means and deflecting means for deflecting a light beam emitted from the light source means two-dimensionally in a first direction and a second directrion, the deflection speed of the deflecting means being higher in the first direction than in the second direction. The deflecting means is driven in such a way that its angular velocity in the second direction is smaller when optically scanning a position on the surface to be scanned at which the angle of incidence of the deflected light beam in the second direction is larger than when optically scanning a position on said surface to be scanned at which the angle of incidence of the deflected light beam in said second direction is small.