PURPOSE: To perform switching at a high speed by connecting a resistor to the emitter of a transistor and setting current feedback so as to prevent more than required base current from flowing.

CONSTITUTION: When pulses for turning a GND1 to an L level are impressed to the base B1 of the transistor TR1, the base current IB1 flows in the H level of the pulses, the transistor TR1 is turned to an ON state and a collector current IC1 which is the multiple of the current amplification factor hfe1 of the base current IB1 flows. Then, by making the collector current IC1 flow in the resistor R2, the output voltage of IC1×R2 is generated at both ends of the resistor R2. In the meantime, an emitter current IE1 (that is IB1+IC1) flows to the resistor R1 on the side of the emitter E1. Thus, the voltage IE1×R1 by a voltage drop is generated at both ends of the resistor R1, the voltage between the base B1 and the emitter E1 drops and the base current IBI is reduced as well. That is, when the base current IB1 is increased and the emitter current IE1 is increased, the current feedback is set so as to lower the base current IB1.