PURPOSE: To obtain the maximum ability of amplifiers at all times, by inputting signals having (n+1) types of frequencies while switching it to 2n sets of power amplifiers, and obtaining the amplified outputs of each frequency from (n+1) sets of output terminals while switching the outputs.

CONSTITUTION: For example, in case of n=2, signals in (n+1) types of frequencies f0∼fn are applied to input terminals 1∼4 of 2n sets of power amplifiers 5∼8 with the time slot as shown in figure. A signal f0 is inputted to the terminals 1∼4 at time slot t0, it is inputted to the terminals 1∼2 at t1, f1 is 3∼4, and f0 is to the terminals 1∼2, f1 is to 3 and f2 is to 4 at time slot t2, respectively. Change-over devices 9∼12, 16, 17 are switched depending on the time slots t0∼t2 and connected to synthesizers 13∼15 and filters 18∼20. This switching is made so that the amplified outputs f0∼f2 can be obtained to output terminals 21∼23 in the output time slots as shown in figure.