In accordance with an embodiment of the present invention, a bandgap voltage reference circuit includes a group of X current sources, a plurality of circuit branches, and a plurality of switches. The enclosure has an exhaust port in a sidewall thereof. The use of the substantially constant radiation without pulsation reduces premature termination of the polymerization. The load is then removed from the transfer unit outside the mine so that it may be advanced back into the mine to retrieve another load. The present invention may be applied to a wireless storage server, wireless headphones, and audio reproduction apparatuses. The jointing holder enables the optical module to reduce the number of components, to be miniaturized, and to reduce the dimensional deviation at the time of the assembly, enabling high-precision assembly.