A mobile station apparatus has established a first bearer that communicates with a home network and a second bearer that communicates with a core network. In the transmission of a multicast join request, the mobile station apparatus transmits the multicast join request by selecting the first bearer if the multicast join request is addressed to the home network, or by selecting the second bearer if the multicast join request is addressed to the core network. In this way, a mobile communication system is provided where the mobile station apparatus connected to a home base station apparatus determines whether a multicast group is based on a Local IP Access and then transmits the multicast join request, and the home base station apparatus appropriately establishes a multicast session to the home network or the core network in response to a determination of the mobile station apparatus.