Abstract: A first high inductor is connected between a ground point and the base of a high frequency amplifying transistor whose emitter is grounded. A first capacitor is connected between a mid-point of the first inductor and the ground point. A second inductor is connected between the collector of the transistor and a power source terminal. A second capacitor is connected between a mid-point of the second inductor and the ground point. The first inductor connects the base of the transistor to ground in a DC mode, and cooperates with the first capacitor to form a first series resonant circuit. The resonance frequency of the circuit is equal to half of the frequency "f" of an input signal to the transistor. The resonant first series circuit allows a signal of the f/2 frequency generated on the base side of the transistor to flow to the ground point. The second inductor feeds electric power to the collector of the transistor, and cooperates with the second capacitor to form a second series resonant circuit.