Polar modulating transmitter and communication device using same

An amplitude modulator (13) modulates the amplitude of a phase modulation signal by an amplitude signal from an amplitude drive unit (12). The power level of the phase modulation signal inputted into the amplitude modulator (13) is regulated by a variable-gain regulator (114). The power level of said phase modulation signal is controlled so as to change continuously. Thus, the amplitude modulator (13) transitions from a saturated operation state to a linear operation state in a continuous manner.