To obtain a treatment advance data of a material to be treated subjected to heating treatment within machinery such as an mirowave oven.

A combination of a sensor 2 for detecting environment temp. and a sensor 3 for detecting reaction temp. is connected to a signal processor 11. The sensor 2 detects the temp. of environment in which a material to be treated is placed and outputs its detection signal to the signal processor 11. The sensor 3 detects the reaction temp. generated by the reaction with moisture of environment in which the material to be treated is placed to output its detection signal to the signal processor 11. The signal processor 11 outputs the signal of the difference between both detection signals. The output signal obtained by the signal processor is the treatment advance data by the heating of the material to be treated.