An optical scanning device configured to remove or sufficiently reduce ghost light includes an input optical system for directing a light beam from a light source to a deflecting surface of a deflector, and an imaging optical system for imaging a light beam scanningly deflected by the deflecting surface upon a surface to be scanned, wherein, in a sub-scan section, the light beam is incident on the deflecting surface of the deflector from an oblique direction with respect to an optical axis of the imaging optical system, wherein a light blocking member for blocking ghost light is disposed on a light path between the deflecting surface and the scanned surface, wherein an end portion of the light blocking member in the sub-scan direction is formed with a curved shape having a height in the sub-scan direction which height changes in accordance with the position in the main-scan direction.