An optical scanning device has a rotary multiple-face mirror, a lens, a housing, and a cover member. The housing has a housing space in which the rotary multiple-face mirror and the lens are housed. The cover member covers the housing space in the housing. The housing has a light emission opening through which a light beam is emitted, and outside the light emission opening in the housing, a light transmitting member which transmits the light beam is provided to close the light emission opening. The cover member has a body part which covers the housing space and a fastening part which fastens the light transmitting member by pressing it toward the light emission opening.