The permeation of the moisture into a case made of metal is roughly perfectly suppressed, and the optical communications of high quality are made possible by the operation of component(s) accommodated in the case. A plurality of through holes through which the outside of the case and a component accommodating portion communicate with each other are provided in the metallic case including a body having the component accommodating portion, and a lid. Fixed components in which an optical fiber ribbon and an optical fiber(s) are respectively sandwiched between associated metallic substrates and associated optical fiber fixing plates to be fixed by solder are fitted into the respective through holes to be hermetically sealed and fixed to the metallic case. One end side of the optical fiber ribbon and the optical fiber(s) which are respectively fixed to the fixed components is inserted into the component accommodating portion of the body to be connected to an input terminal and an output terminal of an arrayed waveguide grating type optical multiplexer/demultiplexer, respectively. The other end side of the optical fiber ribbon and the optical fiber(s) is extracted to the outside of the metallic case.