To construct an economical system by maximizing a system gain by each modulation system in a transmission system to which adaptive modulation is applied.

In an adaptive modulation system for preparing a plurality of modulation systems to change the modulation systems according to traffic fluctuation or transmission conditions, an output back-off is selected by an operating point setting circuit 20 so that the sum of the output back-off and a required signal-to-noise rate can be minimized, and the operating point of a transmission power amplifier 30 in each modulation system is set. In the case of combining transmission power control technologies with the system, the set operating point can be set as the maximum transmission output power.