A reception unit 11 receives transmitted packets. A first available band calculation unit 12 and a second available band calculation unit 13 calculate an available band for a transmission source of the packets. A calculation means determination unit 14 determines, on the basis of the reception states of the packets transmitted at predetermined time intervals in the reception unit 11, whether the first available band calculation unit 12 calculates the available band or the second available band calculation unit 13 calculates the available band. The first available band calculation unit 12 calculates the available band on the basis of a reception interval between the packets. The second available band calculation unit 13 calculates the available band on the basis of a time required for the reception of the transmitted series of packets and the sizes of the series of the packets.