PURPOSE: To make it possible to display the temperature change for a long time by a display part, whose dot number is few, by displaying all the dots in the direction of the temperature axis between the maximum temperature and the minimum temperature, which re measured in a unit time.

CONSTITUTION: A timer is started by a clock signal generator 8, and temperature is measured. The temperature values are stored in a temperature data memory 9 as the maximum temperature and the minimum temperature. The temperature is measured at every specified time interval, which is a unit time, and the new maximum temperature and minimum temperature are stored. Based on these data, all the dots between the maximum temperature and the minimum temperature on the Y (temperature) axis on the coordinate X are lighted on an LCD temperature display part 3. Based on these operations, the maximum temperature, the minimum temperature and the temperature difference for every unit time are displayed on the LCD temperature display part 3 to the final column in the X direction.