An optical connecting apparatus has a light source outputting an optical signal indicating a plurality of wavelengths which correspond to a plurality of transmission channels, an optical transmit section and an optical receive section being mounted with integrated circuits and being connected to each other through an optical line of a single system, and a signal conversion section being inlet in the optical line and converting a phase modulated signal into an intensity modulated signal. The optical transmit section includes: a demultiplexer which separates the optical signal from the light source according to the transmission channels; an optical modulator unit which generates phase modulated signals by implementing phase modulation with optical signals from the demultiplexer by using a plurality of optical modulators whose operations are synchronized by a signal from the integrated circuit; and a multiplexer which multiplexes the phase modulated signals from the optical modulator unit and outputs the multiplexed phase modulated signals to the signal conversion section through the optical line. The optical receive section includes: a demultiplexer which separates the intensity modulated signal from the signal conversion section according to the transmission channels; and an optical receiver unit which converts the intensity modulated signals from the demultiplexer into electric signals.