Radio resources are utilized efficiently and the communication quality is improved by flexibly adapting to the state of radio waves at a base station varying every moment or the topology of the distribution area of contents in multicast communication. The base station (100) stores information including the flow distribution starting time, the error rate measuring period, the threshold in an intra-base station flow management table. When detecting that it becomes the time before the error rate measuring period from the flow distribution starting time, the reception quality of radio terminals in the communication area of the base station (100) is measured. A base station (100-b) where the reception quality exceeds the threshold redundantly transmits multicast data assigned to a plurality of radio resources (800-b1, 800-b3, 800-b5). A base station (100-a) where the reception quality does not exceed the threshold transmits multicast data assigned to a single radio resource (800-a1).