A power amplifier includes: a plurality of field effect transistors connected in parallel and each having a first and second ends, the first end being connected to ground; an amplifying unit which includes at least one of an inductor, a capacitor and a band pass filter and has a third and fourth ends, the third end being connected to the second ends of the field effect transistors, and the fourth end outputting an amplified output signal; and an amplitude controller which sends control signals respectively to gates of the field effect transistors to turn on or off the field effect transistors based on an address signal for performing selection on the field effect transistors and a clock signal. Channel widths of the field effect transistors are different from each other.