PURPOSE: To prevent a damage to the load and ruin of the transistor which drives and controls the load by decreasing the potential at base and collector of the transistor which control the load transistor when the voltage applied to the load exceeds a specified value.

CONSTITUTION: When the DC output voltage applied to the integrated circuit 10 is made so high that it exceeds the voltage of Zener diode 16, a current flows in the resistances 17 and 18 connected with each other in series through the Zener diode 16. By this, base currents flow in the respective transistors 20, 22 the transistor 20 is approached to "on", the potential at base of the transistor 14 reduces and the transistor 14 is approached to "off". Also a base current flows in the transistor 22, which is approached to "on". Thus the potential at collector of the transistor 14 decreases. When the transistor 14 is not operated, the base current is not fed to the transistor 5 which is added to the integrated circuit 10 and drives the load 4, the transistor 5 is turned off. Therefore a damage to the load and the ruin of element can be prevented.