To measure a delay time even when slave station identifying information is not previously obtained by measuring propagation delay time information between a slave station and a self device in the case of automatically obtaining identifying information of the slave station whose identifyinga information is not registered in the self device, obtaining a correction time and permitting the slave station to set it.

When identifying information of the slave station whose identifying information is not registered in the self device is automatically obtained, propagation delay time information between the slave station and the self device is measured, the correction time is obtained, the slave station is made to set it. For example, a main station is provided with an ATM-PON interface circuit 2A which terminates an optical fiber and assumes an interface function with a slave station side. The ATM-PON interface circuit 2A is provided with a receiving part 10, a cell detecting part 11, a delay measuring part 13 and a delay control state managing part 14 or the like. Then the delay measuring part 13 measures the delay time of the slave station based on a prescribed cell which is outputted from the cell detecting part 11 and individually manages a state concerning the delay time of each slave station.