A retransmitting method, a radio receiving apparatus and a multiantenna communication system that are capable of improving the system throughput. According to this method, the receiving apparatus determines whether a received substream has an error and hence a retransmittal is necessary (401); calculates a signal-to-interference noise ratio after detection of multiinput/multioutput of the substream that must be retransmitted (402); compares the signal-to-interference noise ratio of the substream, which must be retransmitted, with a predetermined threshold value (403); performs a full retransmission of the substream, which must be retransmitted, when the signal-to-interference noise ratio of the substream, which must be retransmitted, is smaller than the predetermined threshold value (404); and performs a redundant-increased retransmission of the substream, which must be retransmitted, when the signal-to-interference noise ratio of the substream, which must be retransmitted, is greater than the predetermined threshold value (405,406,407).