To provide a technology for predicting disconnection of a heater wire, composed of a resistance exothermic body which is the heating means installed at the surroundings of a reaction tube, in a device in which semiconductor wafers of numerous sheets are brought into the reaction tube, and heat treatment is carried out.

A serial process in which the wafer is brought into the reaction tube 1 and the heat treatment is carried out, and afterwards the wafer is taken out of the reaction tube 1 in a single operation; and if the time slot, in which temperature is stable before the wafer is brought into the reaction tube 1, is called steady-state temperature time, in the respective time operation, a supplied electric power to the heater wire in the steady temperature is measured. Then, based on this measurement data, the standard deviation in the steady-state temperature time in the respective time of operation is calculated, and further, based on the standard deviation for each operation, the transition of the standard deviation, for example the moving average is calculated, alarm is outputted by forecasting the disconnection of the heater element wire, when this moving average is in an increasing tendency.