To transfer data efficiently, when a mobile communication unit performs data communication and to communicate even a large volume of data at a high rate with a high real-time performance.

A radio control/exchange controller comprises a section 13 for setting a logical connection, a section 11 executing protocol processing having selection retransmission on a logical connection, and a section 12 for managing protocol parameters required for protocol processing where the protocol parameters are set or altered to values suitable for data communication at the communication parameter managing section 12. At this time, by controlling one of the protocol parameters, i.e., the delivery interval of an acknowledgement packet, to an appropriate value throughput is enhanced and release delay of a transmission buffer is reduced.