Provided is a point-to-multipoint optical communication system capable of extending a transmission distance between a subscriber apparatus and a station apparatus without changing wavelengths of an upstream optical signal and a downstream optical signal, which are used in both of the apparatuses. The point-to-multipoint optical communication system includes, as a basic configuration thereof, an optical network for connecting one station apparatus (1) to a plurality of (n) subscriber apparatuses (4). Among m basic configurations, one station-side wavelength multiplexer/demultiplexer (22), one optical fiber transmission line (30), and one subscriber-side wavelength multiplexer/demultiplexer (12) are shared. The point-to-multipoint optical communication system further includes a station-side repeating unit (20) and a subscriber-side repeating unit (10) each including the one wavelength multiplexer/demultiplexer (22 or 12) and m wavelength converters (21 or 11). An optical signal having a conventionally-used wavelength is used between the station apparatus (1) and the station-side repeating unit (20) and between the subscriber apparatus (4) and the subscriber-side repeating unit (10), and an extensible optical signal, on which wavelength division multiplexing has been performed, is used between the wavelength multiplexers/demultiplexers (12 and 22) via the optical fiber transmission line (30).