memory of maximum 811 instead of the original stored value the measured result value is converted into decimal data by hex2bcd hexadecimal estimate converter 812 and through display driver 813 to drive liquid crystal display lcd 814 for showing the temperature value if the measured result value is smaller than the initial value in highest temperature memory 811 a signal is output to make the temperature stability time counter in timing producer 803 increase a unit time but no signal to hex2bcd hexadecimal estimate converter 812 at the same time the measured result value is stored into buffer memory 817 and a signal is output to make the temperature stability time counter in timing producer 803 turn to zero slope calculation buffer memory 819 calculates the difference value between buffer memory 817 and buffer memory 818 the difference value is stored into slope buffer memory 820 then the value of buffer memory 817 is again stored into buffer memory 818 step 908 estimate interval time between two inflexion points as interval time for sweep later at the same time compare varied values of temperature per unit time by means of the climbing slope of temperature per unit time turning from decrease to increase estimate inflexion of temperature.