An optical scanning device includes an optical housing; an elongated optical element arranged in the optical housing and having a shape extending in a main-scanning direction; a retaining member provided at a side opposite to a surface of the optical housing on which the optical element is arranged to maintain an attachment attitude of the optical element in the optical housing; a curvature adjusting unit configured to adjust a curvature of the elongated optical element in a scanning line via the retaining member; a tilt adjusting unit configured to adjust a tilt of the optical element in the scanning line by making the optical element rotate on an optical axis via the retaining member; and a positioning unit configured to position the optical element in the optical axis direction, and provided in the optical housing and having such a shape that the optical element fits the positioning unit.