PURPOSE: To perform the small size, the increase in the reliability, and cost reduction, by using a single active element and a few number of passive elements.

CONSTITUTION: The cathode of the diode D2 normally in forward bias is connected to the positive phase input terminal + of the voltage comparison circuit 30, and the anode of the diode D1 normally in forward bias is connected to the opposite phase input terminal -. Further, the cathode of the diode D1 and the anode of the diode D2 are connected, the connection end is taken as the input terminal of the circuit, and the output terminal of the voltage comparison circuit 30 is taken as the output terminal of the circuit. Thus, the full wave rectifying and rectangular shaping functions can be realized with a single active element (voltage comparison circuit) and a few number of passive elements.