To make a jig structure simple and achieve a reduction in size thereof.

First and second load transmission members 5 and 6 are configured such that a pair of engagement portions 7 and 10 are provided with gaps 8 and 11 for inserting a gauge portion 2 of a tensile test piece 1 interposed therebetween on unilateral side surfaces of leading end portions of load transmission columnar supports 15 and 17 having base ends attached to load receiving plates 14 and 16. Further, space portions 9 and 12 capable of accommodating grip portions 3b and 3a of the tensile test piece 1 are provided between the respective engagement portions 7 and 10 and the load receiving plates 14 and 16 of the respective load transmission members 5 and 6. When a tensile test is performed, a compressive load applied to the respective load receiving plates 14 and 16 is applied to the respective grip portions 3b and 3a of the tensile test piece 1 via the load transmission columnar supports 15 and 17 and the respective engagement portions 7 and 10 as loads in directions separated from each other in a state that leading ends of the engagement portions 7 and 10 of the respective load transmission members 5 and 6 are disposed so as to be brought into contact with the grip portions 3a and 3b of the tensile test piece 1.