To provide a fastening body structure which uses a screw member using a module screw having a screw head in a contersunk screw shape together with a shape memory alloy-made washer, and in which the shape memory alloy-made washer does not expand even if subjected to large fastening force in fastening of a part to be fastened and the shape memory alloy-made washer can be easily removed when the screw fastening is released.

This fastening body structure 1 is provided for fastening the fastening part 10 desired to be fastened and fixed to an installation section, by the screw member 4 having the module screw 2 having a male screw 2d used as a pair with a female screw section 21 arranged in the installation section 20 and the screw head 2a processed into a countersunk screw shape and the shape memory alloy-made washer 3 formed of a shape memory alloy in a dimension corresponding to the module screw. The fastening body structure is constituted by arranging an irregular section 5 (50) on a slope surface of a head part under surface of the module screw or a screw abutting surface of the shape memory alloy-made washer.