An optical scanning apparatus for optically scanning at least one scanning target surface, the optical scanning apparatus including: a light source; a light-flux dividing unit disposed on a main optical path of a main light flux emitted from the light source, and the light-flux dividing unit configured to spatially divide the main light flux; an optical deflector disposed on a divided optical path of the divided light flux, and the optical deflector configured to deflect the divided optical path; an optical path opening/closing switch unit disposed on the divided optical path between the light-flux dividing unit and the optical deflector, and the optical path opening/closing switch unit configured to interrupt or pass at least one of the divided optical path; and a controller configured to control operation of interrupting or passing the at least one of the divided optical path by the optical path opening/closing switch unit.