According to the present disclosure, a light scanning device includes a housing, a light source, a polygon mirror, a polygon motor, a cooling duct, and a fastening portion. The housing is constituted by a housing main body and an upper lid. The light source is supported at one end side of the housing main body. The cooling duct is provided in the housing main body to extend from a light-source side to a side opposite from the light source. The fastening portion is constituted by first and second fastening portions disposed on the light-source side so as to sandwich the light source therebetween and a third fastening portion disposed at a position that is on the side opposite from the light source and that does not overlap the cooling duct as seen from a screw-fastening direction.