In multicast transfer in a passive optical network (PON) system, an optical line terminal (OLT) is provided, which dynamically changes the longest response time included in a General Query message or a Specific Query message to control the timing at which a given terminal device transmits a report message. This reduces the possibility that the OLT has failed in getting some report messages from terminal devices due to lack of processing capability, and reduces the waste of the band due to useless transmission of multicast packets, which is caused by a delay in reporting that the given terminal device has left a multicast group, by taking into consideration both the message processing capability of the OLT and the number of optical network units (ONUs) each of which has terminal devices being subordinate thereto and belonging to the same multicast group.