A base station in a communication system where mobile stations receive paging announce using a discontinuously received reception frame and the mobile stations receive multicast data as well as the paging announce, in which the mobile stations in idle mode are searched for from among the mobile stations receiving multicast data, the mobile stations located where a paging group to which the searched-for mobile stations belong overlaps an area where the multicast data are distributed are selected from among the searched-for mobile stations, and the base station includes a radio resource allocating unit allocating radio resources to the selected mobile stations, the radio resources being for transmitting uplink signal, and an allocated radio resource information including unit including information of radio resources allocated by the radio resource allocating unit in a radio frame transmitting the multicast data to be transmitted to the selected mobile stations.