A first distance is longer than a second distance. This sets a movable plate 653 apart from the horizontal side portions (first adjacent portions) 652a in the direction Y of a pivot axis, which reduces air resistance against the movable plate 653 and hence the amount of heat generation. A light beam from a first optical system impinges upon a deflection mirror surface 651 from the front side of the deflection mirror surface 651 and along the direction Y of the pivot axis at an acute angle with respect to the surface normal to the deflection mirror surface 651. Hence, the light beam L travels in the space other than the space surrounding the deflection mirror surface 651, namely, the space in the vicinity of a central section of the deflection mirror surface. This realizes scanning with the light beam without thermal influence.