PURPOSE: To enable a wafer to be adequately and accurately controlled in temperature by a method wherein the temperature of the wafer processed as prescribed in a reactive vessel is precisely measured.

CONSTITUTION: Probes 26 are provided facing upwards inside probe housing holes 24 (for instance, a pair) which are provided on the top of a lower electrode 16 at predetermined intervals. The probe 26 is composed of a cylindrical probe main body and a probe stylus which protrudes from the probe main body, where the probe stylus is elastically supported in a vertical direction by a spring provided to the base of the probe main body. When a silicon wafer 20 is placed on the lower electrode, the tip of the probe stylus of the probe 26 is contacted with the underside of the silicon wafer 20 under an adequate pressure. The probes 26 are connected to a wafer temperature monitoring device 30 located outside of a reactive vessel 10 through the intermediary of a cable 28 which passes through the lower electrode.