An optical scanning device includes a substrate, a frame, a torsion beam, and a cantilever. The substrate has a three-layer structure including an oxide film sandwiched between two silicon substrates. The torsion beam swingably supports a mirror portion which deflects a light beam projected from a light source. The cantilever is supported by the frame to connect to the torsion beam and applies torque to the torsion beam. The cantilever and the torsion beam are formed on the same silicon substrate. The cantilever has a thickness substantially thinner than the thickness of the torsion beam. An image forming apparatus includes the optical scanning device. An image projection device includes the optical scanning device.