A light beam scanning device deflecting, by using a rotating polygon mirror, a light beam emitted from a light source and condensing, by using a scanning lens, the deflected light beam onto a scanned surface. The light beam scanning device includes: a base made of a metal or a resin; a motor unit attached to the base and rotating the polygon mirror; a holding member holding the scanning lens; and one or more fixing members disposed between the base and the holding member, fixing the holding member to the base with the scanning lens spaced away from the base. In the light beam scanning device, the base has, between at least one of the fixing members and the motor unit, a penetrating hole or groove around which heat transmitted from the motor unit through the base to the fixing member passes.