A base station BS transmits downlink data to a relay station RS. A mobile station MS transmits uplink data to the relay station RS. The relay station RS determines a first modulation scheme for transmitting the uplink data to the base station BS, and determines a second modulation scheme for transmitting the downlink data to the mobile station MS. The relay station RS multiplies a symbol sequence obtained by the first modulation scheme by a symbol sequence obtained by the second modulation scheme for each symbol, and multicasts the multiplication result to the base station BS and the mobile station MS.