The present invention provides an optical access network system that allows the transmission of packets irrespective of the packet length and which is also capable of adapting to cases where another user temporarily requires a large capacity bandwidth. This system performs two-way optical communications using a code division multiplexing system via an optical fiber channel and a star coupler between an optical line terminal and first and second optical network units. The optical line terminal comprises a bandwidth control section and a bandwidth allocation section and the bandwidth control section has signal converter pairs installed therein in a number equal to the number of optical network units. Further, the optical network units each comprise first and second bandwidth control sections and first and second bandwidth allocation sections. The bandwidth control sections each have one set of signal converter pairs installed therein. The bandwidth control sections of the optical line terminal and the optical network units each have a signal converter pair that is constituted by one set of a variable serial to parallel conversion unit and a variable parallel to serial conversion unit each having a variable bandwidth management function.