PURPOSE: To improve power source efficiency by arranging a 2nd lumped constant parallel resonance means which is extremely high to a fundamental wave and extremely low to a 2nd higher harmonic between the output electrode and ground electrode of an amplifying element.

CONSTITUTION: A parallel circuit 8 which cuts off the 2nd higher harmonic and the parallel resonance circuit 9 which is open to the fundamental wave and short-circuited to the 2nd higher harmonic are connected to the output electrode 2 of the amplifying element 1. Therefore, even when a matching circuit for the fundamental wave is connected to behind an output terminal 7, impedance which is nearly open to the 2nd higher harmonic is realized. A short-circuit end point, on the other hand, is nearly aligned with the output terminal 2 of the amplifying element. Consequently, the power consumption originating the 2nd higher harmonic is almost eliminated.