To provide a compacter fastening structure capable of easily cancelling fastening between fastened members while securing sufficient force of fastening the fastened members to each other.

In the fastening structure 10, a split stopper 31 is applied onto the outer peripheries of first and second nut pieces 23, 24 and the split stopper 31 and the nut pieces 23, 24 are fitted into a ring member 25 until the nut pieces 23, 24 are integrated therewith to form a clamping member 20 which is connectable to a bolt 13. The ring member 25 is formed of a shape memory material which produces contractive deforming force with heat, and the ring member 25 has a vulnerable portion 26 breakable when the contractive deforming force is produced. The breakage of the vulnerable portion 26 cancels fastening between the first and second fastened members 11, 12.