The invention relates to a high frequency power amplifier capable of improving strain characteristic. A multi-finger type transistor is formed by connecting a plurality of transistor cells in parallel. Gate electrodes of the transistor cells are connected to an input side matching circuit. Resonant circuits are respectively connected between the gate electrode of a transistor cell and the input side matching circuit. The resonant circuit resonates at a second harmonic of the operating frequency of the transistor or within a predetermined range of frequencies having a center at the second harmonic of the operating frequency, and becomes a high-impedance load at the second harmonic, or an open load.