To provide fastening structure, facilitating fastening work, without causing deterioration in ease of workability in bolt replacement.

The fastening structure 1 has a fastening auxiliary member 4, a bolt 3, and a nut 2. The fastening auxiliary member 4 is fixed on one face of a fastened member 5, while a fastening hole 52 of the fastened member 5 is opened. The bolt 3 is integrally provided with: a bolt head part 31; a bolt shaft part 32 extended from the bolt head part 31; and a projection part 34 disposed on a base end side of the bolt shaft part 32 and projected to the outer side than the bolt head part 31 with respect to the bolt shaft part 32. A tip of the bolt shaft part 32 is inserted into the fastening hole 52 from one face side of the fastened member 5 and is projected on the other face side to be in a state where the fastening can be performed. The fastening auxiliary member 4 has an engagement part 43 abutting on and engaged with a projection part 34 of the bolt 3 rotated in a direction releasing the fastening, in a state where the fastening can be performed, and preventing rotation in the fastening releasing direction of the projection part 34 and movement in a direction separated from the fastened member 5.