PURPOSE: To obtain an output voltage from a threshold detecting circuit in response to an input exceeding a preset threshold inputted to an output node by providing an input node and a current sink and resistance element connected to the input node. CONSTITUTION: A nose 12 receives an input voltage and supplies the voltage to current mirrors through a resistor 32. A first current mirror 16 incorporates an npn transistor Q18 and another transistor Q20 which is N times as large as the transistor Q18, receives a reference current IPTAT, and sucks a current NIPTAT which is N times as large as the reference current IPTAT after mirroring. A second current mirror 22 incorporates an npn transistor Q24 and another transistor Q26 which is M time as large as the transistor Q24, is connected to the first current mirror 16, and mirrors the current NIPTAT. The collector current of the transistor Q26 becomes (M×N)IPTAT. Since a current sink 28 incorporates an npn transistor Q29 and has the maximum sucking current IPTAT, an excessive current (M×N)IPTAT-IPTAT becomes the base current of a pnp transistor Q30 and, when the sucking current of the sink 28 is exceeded, supplies an output voltage level to a node 14. When a threshold detecting circuit is constituted in such a way, the circuit can detect a threshold level exceeding the power supply voltage without relying upon the ambient temperature. COPYRIGHT: (C)1991,JPO