PURPOSE: To detect an abnormal rise in the output voltage of a voltage generating circuit by providing an MOSFET which inputs the potential level on wiring as a gate voltage.

CONSTITUTION: The resistance between the drain and source of the MOSFET 11 becomes large and the voltage at an output terminal 12 becomes closer to the ground level (level 0) as a voltage (VCS voltage) which operates a current switching type logic gate (ECL gate), i.e. the voltage on the wiring drops more. As the VCS voltage rises more, on the other hand, the resistance between the drain and source of the MOSFET 11 decreases and the voltage at the output terminal 12 becomes closer to a VEE power source level (level 1). Consequently, when the VCS voltage rises abnormally, the output terminal 12 of the MOSFET 11 is held at the level 1 and the abnormal rise in the VCS voltage is detected.