PURPOSE: To quantitatively detect acceleration, deceleration, etc. of a car, by converting an input signal to a differential output of a voltage level which is different in accordance with the variation rate, and comparing it with a setting voltage.

CONSTITUTION: An input signal VIN is applied to a differentiator 12 through an amplifier 11, a differential output signal VB whose voltage level is different in accordance with the variation rate of the signal is generated, and it is compared with a setting voltage V2 by a comparator 13. In this case, when the voltage V2 is set to a reference variation rate and is selected to a differential output level corresponding to a variation rate A, a variation rate detecting output signal VOUT from the comparator 13 is reduced to a signal having waveform (c) by the differential output VB. Accordingly, as to the variation rate of the input signal VIN, a quantitative detection can be executed.