To provide a new anti-theft double nut-type fastening tool having both of anti-theft function and a locking function, a new exclusive tool for rotating and operating the anti-theft double nut-type fastening tool, a new anti-theft fastening tool set composed of combination of the anti-theft double nut type fastening tool and the exclusive tool, a new anti-theft nut, and a new nut set.

The anti-theft double nut-type fastening tool including a bolt 1, a first nut 2 and a second nut 3, is provided with a recessed portion 25 for rotating and operating the first nut 2 in a region of a top face portion 22 of the first nut covered with a bottom portion 31 of the second nut when the second nut 3 is screwed to the bolt 1 in a state in which the second nut 3 and the first nut 2 are adjacent to each other.