PURPOSE: To perform optical scanning with high precision by using one scanning mirror and arranging a light source, a lens, and a reflecting mirror in such a way that two laser beams are nearly equal in optical path length and nearly coincident with a normal line of a recording body surface.

CONSTITUTION: The 1st beam 3 and 2nd beam 4 are reflected by a half-mirror 5, or transmitted and synthesized to form an image on a drum 1 through a scanning mirror 6, which scans light by rotating or pulsating, and a scanning lens 7. This constitution synthesizes those two beams extremely closely, and allows one scanning mirror 6 to irradiate the drum with beams which are nearly equal in optical path length and nearly coincident with a normal of the drum surface, performing exposure scanning free of distortion by the inexpensive, simple constitution.