Wireless base transceiver station, communication system and flow control method

A wireless base transceiver station that transmits and receives data to and from an external device via fixed-line communication and transmits and receives data to and from a mobile station via radio communication. The wireless base transceiver station includes a radio communication unit configured to measure radio quality in a radio zone based on an error rate of data received from the radio zone, and a fixed-line communication unit configured to measure the amount of data flow in a fixed-line zone to perform flow control on data in the fixed-line zone. The wireless base transceiver station includes a control unit configured to control the flow control performed by the fixed-line communication unit, based on the amount of data flow in the fixed-line zone and the radio quality in the radio zone that have been measured by the fixed-line communication unit and the radio communication unit.