A scanline curvature correction mechanism includes a holding mechanism to extend in a main scanning direction and hold an optical element in the main scanning direction, a pressing member provided near a center of the optical element in the main scanning direction and press the optical element of the optical scanning device in the sub-scanning direction, and a curvature adjustment mechanism provided on an opposite side of the pressing member with the optical element interposed therebetween and to adjust a curvature of the optical element in the sub-scanning direction. The curvature adjustment mechanism includes an eccentric cam to rotate around a rotation axis parallel to an optical axis of the optical element and include a cam portion of which an outer peripheral surface is eccentric with respect to the rotation axis, and a fixing mechanism to stepwisely fix an angular position of rotation of the eccentric cam.