An optical scanning device, which scans a surface to be scanned by light, includes a light source, a coupling optical system, which changes light from the light source into approximately parallel light, a light control reflection member which is disposed in an optical path of the light from the coupling optical system, the light control reflection member defining a diameter of a beam of the light which scans the surface to be scanned, and reflecting a part of the light which is not used for the scanning toward the coupling optical system, and a light detector which receives the light reflected by the light control reflection member via the coupling optical system.