A laser scanner which includes a rotary polyhedral mirror for scanning a light beam from a laser light source, and an F.theta. lens system which includes first and second lenses through which the light beam is radiated onto a scanning plane. The first lens of the F.theta. lens system is provided on the rotary polyhedral mirror side and is constructed with a joined lens, to increase the degree of design of the first lens. This design freedom for the F.theta. lens system improves the F.theta. characteristic (i.e., characteristic of displacement on a scanning plane), the field curvature characteristic (i.e., characteristic of image defocusing on the scanning plane) and similar problems.