A message-type determining unit determines whether an IGMP message received from a user terminal is a join message. A table controlling unit determines that a connection needs to be established when receiving a join message from a user terminal. The table controlling unit determines that a connection needs to be removed when all the user terminals have left a multicast group. A CID obtaining unit obtains the CID of a connection to be established or removed. A C control-message generating unit generates a C control message to request connection establishment or connection removal. A C control-message transmitting unit sends the C control message to an OLT.