An optical scanning apparatus includes a light source; a deflection scanner for scanningly deflecting a laser beam emitted by the light source; a deflection member for deflecting a part of the laser beam emitted by the light source, the deflection member being disposed between the light source and the deflection scanner; a common sensor for receiving the laser beam emitted by the light source; wherein the common sensor receives both of the laser beam deflected by the deflection member before it is incident on the deflection scanner and the laser beam scanningly deflected by the deflection scanner.