To provide a fastening structure of a structural material using a high-strength bolt, controlled to high quality regardless of work environment, and advantageous to lowering the cost and labor-saving.

A disc spring 24 has a nonlinear characteristic of relationship between the compressive force F and the deformation amount S, so that it enters a third compression deformed state in which the compressive force F exceeds the introduced tension before it enters a fourth compression deformed state in which the spring is completely crushed by the compressive force F not to elastically deform any more. The disc spring 24 is formed so that the inclination of a curve of the nonlinear characteristic becomes smaller from when the compressive force F exceeds the introduced tension. In the disc spring 24, a shaft part 2004 is passed through a center hole 2402, a tool is inserted in a fastening hole 2006, and a nut 22 or the shaft part 2004 is turned to fasten the nut 22 to the shaft part 2004, so that the disc spring is compressed in the third compression deformed state between the nut 22 and the surface 1202 of a structural material 12.