An image forming apparatus includes an optical scanning device including a light source element configured to radiate a light beam, an optical deflector configured to deflect the light beam two-dimensionally, and a target scanning surface that is transparent and having a two-dimensional image formed thereon by the light beam deflected from the optical deflector, and a projection optical system including a convex mirror and configured to enlarge and project the two-dimensional image on a target projection surface. The target projection surface includes a reflection surface of a half mirror. The half mirror is positioned outside of the image forming apparatus and configured to transmit a part of a light incident on the half mirror and reflect another part of the light incident on the half mirror.