Provided is an optical access system comprising: an optical line terminal connected to another network; a plurality of optical network units, each connected to a user terminal; and at least one of an optical switching unit and an optical splitter, which is installed between the optical line terminal and the plurality of optical network units. The optical line terminal allocates a length of time to a discovery phase for detecting the plurality of optical network units, and a length of time to data transmission phases for transferring data from the plurality of optical network units; and changes a ratio of the length of time of the discovery phase to the length of time of the data transmission phases so that the length of time of the discovery phase is shortened in the case where a number of the optical network units that are registered in the optical line terminal increase.