PURPOSE: To make it possible to measure accurate temperature, by correcting the difference between the temperature detected by a temperature sensor and the actual temperature through an external switch after the completion of assembling of parts, and displaying the accurate value.

CONSTITUTION: A temperature sensor 20 detects the temperature of a completed body, and a signal having a frequency corresponding to said temperature is outputted. Said signal is made to pass an AND gate 23 for the time period, which is controlled by a counter 21, and counted by a sensor counter. The result is converted into a temperature value by a data processing circuit 24 and displayed on a display part A. When a difference exists between said temperature and the actual temperature, the data for correcting said difference is set in a preset circuit 25. In this way, the contents of the sensor counter 22 are corrected, and the accurate temperature value is displayed on the display part A.