Abstract: A radio frequency amplifying apparatus including a radio frequency amplifying circuit operative in response to a signal of high frequency wave generated from a source generator includes a switching circuit operatively connected to the source generator and generating an excitation signal in response to the signal from the source generator and a vacuum tube provided with a control grid to which the excitation signal from the switching circuit is inputted. The source generator generates a trigger signal and a switching frequency of the switching circuit is changed by changing a frequency of the trigger signal. An insulation transformer is disposed between the source generator and the switching circuit and a bias power source is connected to the switching circuit.