PURPOSE: To reduce error due to noise, etc., by comparing a counter output after being converted into an analog value with an input signal, inputting a clock pulse to a register according to the output of comparison, and completing the measurement when the counter makes full-count.

CONSTITUTION: A counter 4 and a register 12 are cleared and a clock generator 3 generates a clock. This clock is counted by a counter 4, the count value is converted into an analog value with a D/A converter 2 and applied to a comparator 1. A temperature data (b) is applied to the comparator 1 and the register 12 counts the clock until the output of the D/A converter 2 is greater than the temperature data. When the counter 4 makes full-count, a gate 5 is opened and the operation of the clock generator 3 is stopped. If any noise is present, since the comparator 1 only inverts, the error of the register 12 is reduced.