PURPOSE: To simplify operation, to improve mounting efficiency and to omit the protection of an optical connector, by connecting electricity and light in the plug-in system simultaneously with the loading of a block to a frame.

CONSTITUTION: An optical plug 18 is fitted to the frame 11 through an electric connector 16 and an optical housing 17. A unit 14 is accommodated in the block 12 so as to be freely slided, and an electric connector 15 and a connector 16' to be connected to the electric connector 16 fitted to the frame 11 are mounted on a back board 13. The unit 14 is provided with an electric connector 15' and an optical jack 20. When the unit 14 is to be accommodated in the block 12 in said constitution, the connectors 15, 15' are plugged in. At the mounting of the block 12 on the frame 11, the connectors 16, 16' are plugged in a plug 18 and the jack 20 are also plugged in, so that electricity and light are simultaneously connected.