PURPOSE: To prevent the transient response of a voltage value detecting circuit from being extremely delayed by changing an input signal and separating the input terminal voltage of a comparator sharply from a dynamic range.

CONSTITUTION: When the input voltage of an input terminal 6 of a voltage comparator consisting of transistors (TRs) 7, 8 is included in a normal operation range (dynamic range), an output from the collector of the TR8 is applied to a TR18 connected to the collector of the TR7 in series to connect the TR18. Therefore the collector of the TR18 has almost the same potential as earth potential and the TR18 operates the same manner as a circuit excluding the TR 18 and a resistor 17. When the voltage of the input terminal is reduced and the voltage of the terminal 19 is turned to about 0.7V, the TR18 is turned off. Consequently the emitter current of the TR7 is made flow into the base and the voltage of the input terminal 6 rises. Even if the input signal is not applied, the input terminal 6 of the voltage comparator is approximately held at the limit point of the dynamic range.