An optical scanning apparatus includes a laser source configured to irradiate a laser beam, a prism configured to reflect the laser beam irradiated from the laser source, a mirror configured to move the laser beam reflected from the prism by oscillating with respect to a predetermined axis and reflecting the laser beam reflected from the prism, the laser beam reflected from the prism being substantially perpendicular to a plane of the mirror in a case where the mirror is in a non-oscillating state, a waveplate positioned between the prism and the mirror and configured to polarize the laser beam reflected from the prism and the laser beam reflected from the mirror. The waveplate includes an end plane inclined with respect to the laser beam reflected from the prism to the mirror.