1. A multi-antenna communication method comprising: calculating reception quality of a substream requiring a retransmission; determining whether or not there is a transmission antenna that will satisfy a target reception quality if used in the retransmission of the substream, from among candidate transmission antennas for use in the retransmission of the substream; and if there are transmission antennas that will satisfy the target reception quality from among the candidate transmission antennas for use in the retransmission of the substream, selecting a transmission antenna showing poorest channel characteristics from among the transmission antennas that will satisfy the target reception quality and designating the selected transmission antenna as an antenna to be used in the retransmission of the substream, and, if there are no transmission antennas that will satisfy the target reception quality from among the candidate transmission antennas for use in the retransmission of the substream, selecting a transmission antenna showing best channel characteristics from among the candidate transmission antennas for use in the retransmission of the substream as the antenna to be used in the retransmission of the substream.