A light beam adjusting device includes a housing having a reflector, a light device disposed within the reflector for generating light which may be partially reflected upwardly and partially reflected downwardly by the reflector. The light reflected downwardly by the reflector is allowed to emit out through the housing. A panel is disposed in the lower portion of the housing, and an actuating device may move the panel to selectively open and block the lower portion of the housing, and to selectively open and block the light reflected upwardly by the reflector. The light reflected upwardly by the reflector may form a high beam together with the light reflected downwardly by the reflector when the lower portion of the housing is not blocked by the panel.