PROBLEM TO BE SOLVED: To prevent the occurrence of loss even when antennas of respective reception systems are installed separately from each other when synthesizing radio signals sent by a plurality of reception systems. SOLUTION: A signal processing part 300 of each reception system not only converts a received radio signal to digital data but also generates gain control data and performs such control by the gain control data that an average amplitude of the radio signal amplified by a radio part 200 is fixed, and outputs the gain control data together with the digital data. A digital synthesis circuit 400 captures data output from each signal processing part 300, through a digital transmission line and synthesizes the digital data and the gain control data out of the captured data into one. Digital data output from the digital synthesis circuit 400 are converted to a radio signal, and then its amplitude is controlled to a fixed gain on the basis of the gain control data output from the digital synthesis circuit 400. COPYRIGHT: (C)2009,JPO&INPIT