A retransmission control method of a transmission-side communication apparatus, which transmits a packet to a reception-side communication apparatus in a radio communication system that supports adaptive modulation and coding (AMC) and hybrid automatic retransmission control (HARQ), comprises: a step (S110 to S125) of transmitting an initially transmitted packet to the reception-side communication apparatus by using a first MCS; and a step (Step S155) of transmitting a new initially transmitted packet to the reception-side communication apparatus by using a second MCS, instead of transmission of a retransmitted packet that is combined with the initially transmitted packet in the reception-side communication apparatus, when the second MCS different from the first MCS is used at the time of retransmission (step s150; NO), the new initially transmitted packet including retransmission data to be transmitted through the retransmitted packet.