To set an object to be measured to a fixed constant temperature within a short time by tightly arranging a stone plate in close contact with the upper surface of a metal plate tightly fixed on the lower surface of an electronic cooler with a built-in thermo-module via a heat conductive material so as to maintain smoothness, wearing resistance and precision for a long time.

A surface plate 1 is constructed in such a manner that a flat stone plate 5 is tightly fixed to the upper surface of a metal plate 3 on whose lower surface an electronic cooler 2 is tightly arranged via a heat conductive material 4 and heat insulating materials 6 are attached to the side peripheral face of the metal plate 3 and the lower surface of the same. The electronic cooler 2 connected the cooling surface of a thermo-module 2B composed of an electronic cooling element to a cooling plate 2A made of metal and heat radiating fins 2C and 2D to its heat radiating surface and this cooler 2 is tightly fixed to the metal plate 3. Wen a fixed temperature is set by operating the input part 8A of a thermostat 8, the digital value of this fixed temperature is displayed on a display part 8B, the current detected temperature of a temperature sensor 9 is also displayed, the cooling plate 2A is cooled by the thermo- module 2B and the stone plate 5 is automatically cooled down to the set temperature.