To provide a measurement data detecting device low in cost and high in reliability that temperature in a furnace can be controlled with high accuracy.

This device is equipped with a V/F converter 16, an 8-bit A/D converter 17, and an arithmetic circuit 18. Temperature in the electric furnace A for dentistry is measured by a thermocouple 11 provided in the furnace. An analog voltage measured by the thermocouple 11 is converted into a frequency signal proportional to the analog voltage and outputted by the converter 16. The analog voltage outputted from the thermocouple 11 is digital-converted by the converter 17. The arithmetic circuit 18 compares the frequency signal outputted from the converter 16 with the digital signal outputted from the converter 17, computes a correction coefficient from an error between the two signals, renews the correction coefficient each time a digital signal is outputted from the converter 17, corrects the frequency signal outputted from the converter 16, and outputs it as a detection signal.