PURPOSE: A high frequency power amplifier with a drain bias modulation circuit is provided to control a drain bias voltage of a transistor in two or more levels without a limit of power capacity. CONSTITUTION: A high frequency power amplifier includes a drain bias modulation circuit (100) and a power amplifier (200). The drain bias modulation circuit outputs a voltage corresponding to a power voltage or multiples of the power voltage according to the size of an input signal. The drain bias modulation circuit includes a transistor and an envelope detector (110). The transistor applies the power voltage to a drain and connects a source to a drain of an amplification transistor. The envelope detector detects the size of the transistor and the input signal and inputs the same to a gate of the transistor. The power amplifier applies an output voltage of the drain bias modulation circuit to the drain and includes the amplification transistor which amplifies and outputs the input signal inputted to the gate. [Reference numerals] (110) Envelope detector