In a data communication system, the function of automatic repeat request is provided for transmission of packets based on a data communication protocol such as the Real-Time Transport Protocol or the User Datagram Protocol. Lost packets are detected at various timings, for example, when the beginning packet of each frame is received, the final frame of each frame is received, at a time limit of processing, and at a regular interval, and retransmission requests are issued accordingly. A data reception terminal does not issue a retransmission request if associated retransmission data will not be in time for playing with consideration of processing time and roundtrip time, thereby avoiding the transmission of useless retransmission request packets and retransmission packets.