To provide a power amplifier that can improve the efficiency.SOLUTION: In a power amplifier 10, an amplification unit 16 amplifies an input signal and outputs the amplified signal from an output terminal T2. An inductive element 18 has one end to which a power supply voltage is supplied and the other end connected to the output terminal T2. The power supply voltage is set such that the reciprocal of the real part of the optimum load admittance of the amplification unit 16 whose output characteristic has a predetermined characteristic is substantially equal to the predetermined characteristic impedance. At the frequency of the input signal, the imaginary part of the admittance of the inductive element 18 is substantially equal to the imaginary part of the optimum load admittance.SELECTED DRAWING: Figure 2