A high-output electric power amplifier using a depression-type FET includes a drain voltage supply portion adapted to create a positive voltage to be applied to a drain terminal in the depression-type FET, and a gate bias voltage supply portion adapted to create a negative voltage to be applied to a gate terminal in the depression-type FET, wherein the drain voltage supply portion uses an external commercial power supply as an electric power source, and the gate bias voltage supply portion uses a battery as an electric power source, in order to certainly prevent breakdowns of the FET due to excessive electric currents.