PURPOSE: To perform a tension test of a sample that was put under a wet and hot condition of high temperature and high pressure by preparing a pair of sample supporting tools in a pressure vessel and by connecting a tension device via a rod passing through a slidably and airtighly with one side of the vessel.

CONSTITUTION: By keeping a sample 19 with sample supporting tools 2, 3 by enclosing in a pressure vessel 1 steam or hot water, and by actuating a tension device, a tension rod 12 is pulled downward. Just then, a tensile load is transmitted via a sample holding tool 3 located under a tension rod 14 and a sample 19, and a sample holding tool 2 placed above the rod 14 and a coupling rod 4 to a displacement detecting rod 5, a coil spring 7 is bent and the desplacement detecting rod 5 is displaced below. The displacement is detected with a detecting means 14 and in an arithmetic device 15 a tension load is operated. When with an increasing tension load, reaction force against the coil 7 exceeds a certain constant value, the sample 19 is elongated, so a travelling distance of the tension rod 12 is detected with a detecting means 16, the detected signal and a tension load from the arithmetic device 15 are sent to a measuring device 17, and a relation between the tension load and elongation of the sample 19 is measured.