PURPOSE: To remove a large ripple component of an analog input signal while obtaining an output signal without time delay, by outputting the proper combination of a preceding value and a current value.

CONSTITUTION: A subtraction is operated with a subtractor 4 between the current value 2 of an output signal obtained from a sensor 1 and the preceding value 31 obtained from a holding circuit 3. The difference signal 5 thereof is compared with a reference value 71 from a reference source 7 by a comparator 6. Here, when the difference signal 5 is larger than the reference value 71, a changeover signal 61 is sent out and a signal 31 of the preceding value as output of the holding circuit 3 is sent to the next stage as output signal 8 with a changeover unit 10. When the difference signal 5 is smaller than the reference value 71, the signal 2 of the current value is sent to the next stage as output signal 8 with the changeover unit 10. As a result, when a ripple exists in the output of the sensor, the preceding value is held while when no ripple exists, the instantaneous value thereof is obtained.