A classifying-synthesizing transmission method of multi-user feedback information at a base station. At the base station, a classifier (554) classifies users into a plurality of kinds on the basis of different efficiencies at the time when the base station transmits information to the users. On the basis of the characteristics of synthetic data, a compressor (555) compresses the information synthesized, to reduce the quantity of information to be transmitted. A synthesizer (556) again synthesizes the compressed data of different user kinds. An encoder (557) adds redundant information to the feedback information to be transmitted. A transmitter (524) transmits the encoded feedback information to all users. As a result, the quantity of communication of a downward feedback channel can be drastically reduced to spare the use of radio resources.