A wiring is located on a multilayer ceramic substrate. A ceramic block is located on the multilayer ceramic substrate. Electronic parts, including a semiconductor laser, are located on a surface of the ceramic block. A wiring located on the surface of the ceramic block connects some of the electronic parts to the wiring. A metallic cap with a glass window is located on the multilayer ceramic substrate. This metallic cap covers the ceramic block and the electronic parts, including the semiconductor laser.