Abstract: An input drive apparatus of a power transistor is constituted by a transformer having a core with an air gap, a primary winding energized from an input source in accordance with a forward input bias instruction, and a secondary winding, a first transistor electrically insulated from the input source and turned ON by the voltage of the secondary winding for supplying a forward input bias to the power transistor, and a second transistor electrically insulated from the input source and turned ON in accordance with a reverse input bias instruction for supplying electromagnetic energy stored in the transformer to the input electrode of the power transistor to act as a reverse bias current in accordance with a reverse bias instruction.