In a transmitter of the present invention, a modulated signal is separated into an amplitude component and a phase component which are inputted to a radio-frequency modulated signal input terminal and a supply voltage terminal of a radio-frequency power amplifier. A voltage adjustment circuit is provided between an output terminal of the radio-frequency power amplifier and an amplitude amplification circuit having a feedback circuit. The voltage adjustment circuit changes the amount of isolation in accordance with the voltage level of the amplitude component. By this, the amplitude component of the radio-frequency modulated wave attenuates the level inputted to the feedback circuit of the amplitude amplification circuit through the supply voltage terminal of the radio-frequency power amplifier.