To increase the number of channels by mode converting capability and mode selecting capability by utilizing the inter-mode incoherence of light by providing a mode converter, an N×1 coupler, a 1×N distributor, and a mode selector.

Light signals outputted form N sets of optical transmitters 401 and 402 have their own single modes M1-MN. The respective light signals are inputted to mode converters 403 and 404. The N mode-converted light signals (M1')-(MN') are passed through the N×1 coupler 405 and 1×N distributor 406 and then distributed to N and sent to N mode selectors 407 and 408. The respective mode selectors 407 and 408 pass only select modes among N modes. When the modes converted by the mode converters 403 and 404 are adjusted to the same modes as the select modes of the mode selectors 407 and 408 before optical receivers 409 and 410 which are to couple the modes, the arbitrary optical transmitters 401 and 402 and arbitrary optical receivers 409 and 410 can be coupled.