To surely prevent decrease in communication function caused by deterioration of optical elements, condensation, etc., for inexpensive cost due to a simple structure by automatically aligning an optical axis of an optical system of one side member or the other member with that of optical elements of a substrate for the optical elements.

Each guide pin 7, 8 of MPO connector 6 is inserted into guide pins 3, 4 of Si substrate 2, and MPO connector 6 and MPO adapter are connected with each other. At this moment, Ferrule of MPO connector 6 comes into direct contact with micro lenses of micro lens array, and each optical fiber on MPO connector side, each micro lens of the micro lens array 11, each optical path window 5 of Si substrate, and each photodetector on a photodetector substrate 16 are precisely aligned on a same optical axis. Therefore, an optical signal transmitted through each optical fiber is made incident on the micro lenses from each ferrule to be converged, and is made incident on each photodetector via each optical path window 5.