PURPOSE: To check a heat generating element from operating under the non-control condition by operating a gate circuit under normal state by another low voltage being lowered from a high voltage during the lowering of a low voltage to prevent malfunctioning of an output transistor.

CONSTITUTION: When the lowering of a low voltage from a terminal 2 is detected, a switch of a power source circuit 7 is changed over with a voltage detection circuit 9 for a low voltage power source and a low voltage is supplied to a gate circuit 3 from a voltage lowering circuit 8 for lowering the high voltage from a terminal 20. Consequently, the circuit 3 operates normally to generate a low level output without the supply of the power to a logic circuit 1 and an output transistor 5 is turned OFF through a level shifter and a buffer circuit 4 to prevent malfunctioning. Thus, a heat generating element 6 is checked from operating under the non-control state thereby eliminating breakdown of the element 6 due to overcurrent.