A semiconductor laser diode module in which a laser diode and an optical fiber are optically coupled with each other efficiently irrespective of an ambient temperature change within the laser diode module. The laser diode module includes a laser diode, an optical system including an optical fiber and a lens portion, a holder configured to receive a portion of the optical system, a base having a holder mounting member and a fastening member, and a bottom plate configured to support the base. The holder is mounted to the fastening member at a first joint position, and the fastening member is mounted to the holder mounting member at a second joint position, where the first and second joint positions are located at substantially a same distance from the bottom plate. Alternatively, the first and second joint positions are coplanar with an active layer of the diode. Alternatively, the holder is mounted to the fastening member at a plurality of first joint positions, and the fastening member being mounted to the holder mounting member at a plurality of second joint positions, where the plurality of first and second joint positions are coplanar.