In a first mode in which the power level of a transmission output signal (S6) is to be high, an output from the multiplier (2) is input to an amplitude modulation signal amplifier (4), and a radio frequency power amplifier (5) performs amplitude modulation on a radio frequency phase modulated signal (S4) using a nonlinear area with a supply voltage from the amplitude modulation signal amplifier (4). In a second mode in which the power level of a transmission output signal (S6) is to be low, the output from the multiplier (2) is input to a variable gain amplifier (7), and the variable gain amplifier (7) performs amplitude modulation on the radio frequency phase modulated signal (S4). The amplitude modulated signal is output without passing through the radio frequency power amplifier (5).