The control unit 11 executes, by using information relating to a transmittable data amount, traffic control on data transmitted from the communication terminal 50. Traffic control may be achieved by fine-tuning, to an appropriate value, a transmission rate applied to transmission of data, based on information relating to a transmittable data amount. In this case, the control unit 11 may raise or lower, from a current value, a transmission rate applied to transmission of data exceeding the transmittable data amount, in such a way as to satisfy the transmittable data amount. Moreover, traffic control may be refusing transmission of data exceeding the transmittable data amount, when a total of data transmitted from the communication terminal 50 exceeds the transmittable data amount. In such a case, the control unit 11 may not perform transmission of data exceeding the transmittable data amount. Alternatively, traffic control may lower, from a current value, a transmission rate applied to transmission of data exceeding the transmittable data amount, when a total of data transmitted from the communication terminal 50 exceeds the transmittable data amount.