PURPOSE: To facilitate temp. control and to precisely obtain a desired temp. even if the temp. difference between a sample part and refrigerant is small by controlling a sample temp. by a change in the transfer resistance of a thermal conductor connecting the sample part and the refrigerant.

CONSTITUTION: A cooling rod 6 is deeply inserted into a tubular cooling rod 14 and the contact area thereof increases when a vessel 11 is moved upward. This area decreases when the vessel is moved downward. The transfer resistance of heat decreases with an increase in the contact area and increases with a decrease therein. The quantity of the heat which is deprived of in the refrigerant 12 in the vessel 12 by being transferred from the sample part 4 to the cooling rods 6 and 14, therefore, increases when the vessel 11 is moved upward and said quantity decreases when the vessel is moved upward. The temp. of the sample is, consequently, decreased by rising the vessel 1 and is increased by lowering the vessel if specified current is held applied to an electric heating wire 5.