To provide a disassembling device for a fastening member, which can easily and quickly remove the fastening member fastened to parent materials without impairing the parent materials, and provide the fastening member to be easily disassemled by the aforesaid disassembling device.

When a blind rivet 10 is to be disassembled by a drilling bit 22 disposed to an electrically driven drill 21, cutting is carried out along the boundary area in the barrel axial direction of the barrel part 11b and flange part 11c of the blind rivet 10 while associate turning is being prevented by pressing the flange part 11c of the blind rivet 10 by a rotation prevention mechanism 23, and the flange part 11c is thereby parted from the barrel part 11b, so that the blind rivet 10 fastened to parent materials 1 and 2 can thereby be made removable.