A check-frame receiving unit receives a check frame containing bandwidth data of a bandwidth allocated to a communication between a transmitting side and a receiving side. A bandwidth-data extracting unit extracts bandwidth data in the check frame and outputs a received bandwidth with a MAC address in the check frame. A bandwidth comparing unit reads out preset bandwidth set in association with a destination MAC address from a bandwidth storing unit, and compares the received bandwidth with the preset bandwidth. A response-frame generating unit generates a response frame containing a result obtained by comparing the received bandwidth with the preset bandwidth, the received bandwidth, and the preset bandwidth. A response-frame transmitting unit transmits the response frame generated by the response-frame generating unit.