PURPOSE: To miniaturize the testing device so as to improve the economical efficiency, and to enable the visual observation of the condition of the material to be tested in a liquid vessel from outside by utilizing the high heat insulating effect of a multilayer tube, which is formed by alternately arranging glasses and air layers, and the transparence of the glass.

CONSTITUTION: Multiple layers of glass tubes 2 are arranged outside of a glass container 1, and the upper and the lower of the glass container 1 is sealed by a heat insulating material 4, and each clearance between the glass tubes 2 is formed into a dry air layer 3. The heat inside of a liquid vessel is alternately transmitted through the glass layers and the air layers 3, and transmitted to the outside. A sample cage 7 is hoisted by a cantilever hook 10 of a flat belt 9 wound around a bobbin 8, and elevated by the drive of an elevating motor 12, and a spline rail 11 is horizontally moved with the bobbin 8 between a high temperature liquid vessel 5 and a low temperature liquid vessel 6 by a moving motor 16. Dry and cold air is supplied to the top surfaces of the liquid vessels 5, 6 from an air curtain nozzle 17, and sucked by a suction port 18. Agitation inside of the liquid vessels 5, 6 is performed by rotating a propeller 19 with an agitating motor 20.