Passive optical fiber net of loop of multiple wave length light generated by utilizing central location

A passive optical network includes a central office (200) and a subscriber-side apparatus (310) connected with the central office (200) through an optical fiber link (300). The subscriber-side apparatus (310) performs communication with the central office (200) based on wavelength-division-multiplexed optical signals. The central office has a routing section (210), provided with first to fourth multiplexing ports (L1,RN,LN,R1), for demultiplexing multi-wavelength light inputted from the fourth multiplexing port (R1) into a plurality of channels (L1,LN,1). Each of the demultiplexed channels (L1,LN,1) is amplified and multiplexed for output through the first multiplexing port (L1). Optical signals inputted through the third multiplexing port (LN) are demultiplexed and outputted upstream. The routing section also multiplexes channels for downstream optical signals, outputting the multiplexed channels through the second port (RN). A splitting section (250), provided with first to third splitting ports and arranged on a loop optical waveguide connects the first (L1) and fourth (R1) multiplexing port with each other. The splitting section (250) causes some of multi-wavelength light inputted into the first splitting port to be outputted through the second splitting port and causes the remainder of multi-wavelength light to be outputted through the third splitting port connected with the fourth multiplexing port (R1). A circulator (260) causes the multi-wavelength light inputted through the second splitting port to be transmitted to the subscriber-side apparatus (310) and causes upstream optical signals received from the subscriber-side apparatus (310) to be outputted to the third multiplexing port (LN).