To provide an optical scanner in which a bow of scanning lines caused thereon when a light beam scanned for reproducing including image information for writing an image is made incident diagonally on a reflection face of a deflection means, is suppressed with an appropriate and inexpensive means.

A cylindrical mirror 15 housed in a mirror holder 20 by being supported by a holding frame 21 is point-supported by supporting projected parts 23 at a face side of both end parts in a longitudinal direction, an adjustment screw 25 is engaged with the part of the holding frame 21 facing to an intermediate part on the other face side in the longitudinal direction, a force diffusion plate 26 is inserted between the adjustment screw 25 and the cylindrical mirror 15. The cylindrical mirror 15 is bent and deformed when the intermediate part of the cylindrical mirror 15 is pressed and moved via the force diffusion plate 26. A bow figure is reduced by making use of the deformation for correcting the bow.