An attachment lens is arranged in a stage subsequent to a scanning lens. After a laser beam is converged by the scanning lens, the laser beam is converted into a parallel beam by the attachment lens. When the scanning lens is displaced in a direction perpendicular to an optical axis of the laser beam, a traveling direction of the laser beam is bent by a predetermined angle immediately after the laser beam passes through the scanning lens. Then, the traveling direction of the laser beam is further bent by a predetermined angle in the same direction by the passage of the laser beam through the attachment lens. Accordingly, a final swing angle of the laser beam outgoing from an outgoing window is increased by a swing angle imparted by the attachment lens compared with the case where the attachment lens is not arranged. One of lens surfaces of the attachment lens is formed in a toroidal surface, which allows the laser beam to have a long outline in a vertical direction.