PURPOSE: To sharply change the temp. of a plate to desired temp. by providing a plurality of thermostatic tanks controlling the temp. of a heating medium, a circulator circulating the heating medium and a valve changing over the connection of the circulator, piping and the respective thermostable tanks.

CONSTITUTION: Piping 5 allowing a heating medium to flow is applied to a plate 2 on which a sample 1 is placed and the heating medium is circulated by a circulator 3. A plurality of thermostatic tanks 4 are provided and the heating media set to predetermined temps. are put in the thermostatic tanks 4. A valve 6 changes over the connection of the piping 5 of the plate 2 and the respective thermostatic tanks 4 and, simultaneously with the changeover of the valve 6, the heating medium of certain temp. flowing to the plate 2 can be altered to the heating medium having different temp. By this constitution, the temp. of the plate 2 can be sharply changed and can be rapidly set to desired temp.