Abstract: A testing apparatus (dynamic thermomechanical analyzer) for analyzing a change of the state of a sample from a fluid state to a solid state. The dynamic thermomechanical analyzer includes: a) a vessel in which the sample is set; b) a spring standing in the vessel; the top of the spring rising above the surface of the sample; c) an oscillator for oscillating the spring via a push rod with a constant amplitude of force; and d) a displacement detector for detecting the displacement of the spring or the push rod. When the spring is oscillated at a constant amplitude of force, the amplitude .DELTA.L of the displacement of the push rod decreases as the initially fluid sample solidifies.