<p>An optical beam scanning system is constructed with less optical elements. A light beam (B1) of parallel rays passes through a first image forming system (L1). The first image-forming system consists of a cylindrical lens (2) having a refracting power in a direction equivalent to a main scanning direction (X) and a spherical convex lens (3). Focuses of the cyiindrical lens and the spherical convex lens are within a prescribed allowance. A light beam (B11) passing through the spherical lens has a character of parallel rays within a vertical plane and a character of convergent rays within a horizontal plane to be focused on a deflection surface (4a). A reflected light beam (B2) is finally focused on a surface-to-be-scanned (8) through a second image-forming system (L2).</p>
