The present invention is composed of a mainframe 2 having a holder portion 2a for detachably holding an optical plug provided on an optical fiber end portion. An input/output board 6 is disposed on the lower side of the mainframe 2, and on the lower face of the input/output board 6, there is provided an electrode portion enabling electric connection by contact pressure. On the lower side of the mainframe 2, there are provided support portions 12, 13 and a peripheral portion 9 protruding downward from the lower face of the input/output board 6, and with use of a screw hole 7 provided on the side of the holder portion 2a of the mainframe 2, the mainframe 2 is fixed to a mounting board 21 with a screw 31.