To provide a fastening element structure wherein a shape memory alloy washer is not widened even if a large fastening force is applied when a fastening part is fastened by using a screw member to be used together with a module screw having a screw head part in a flat head screw shape provided for a male screw part paired with a female screw part and the shape memory alloy washer.

The fastening element structure 1 fastens the fastening part 10 which is to be fastened and fixed by the screw member 4 consisting of the module screw 2 having the male screw 2d used as a pair with the female screw part 21 provided in an installation surface 20 and the screw head part 2a processed in a flat-head screw shape and the shape memory alloy washer 3 composed of a shape memory alloy in a C-shape in a dimension corresponding to a shaft diameter of the male screw part of the module screw and a diameter of the screw head part via the female screw in the installation surface by communicating the module screw in a hole for a screw of the fastening part. A friction torque generation part 12 is provided to generate friction torque for the module screw.