To prevent a fastening screw for fastening electric cables from falling off and to restrict the behavior of ends of the electric cables.

A screw fall-off prevention device 1 prevents fall-off of the fastening screw 101 fastening the ends of the electric cables 200 to a terminal base 100 in attaching or detaching the electric cables 200 to/from the terminal base 100. The screw fall-off prevention device 1 includes: a supporting part 2 that can be disposed in the ends of the electric cables 200; a screw retaining part 3 that is formed in one end of the supporting part 2 and can turnably retain the fastening screw 101; and an electric cable retention part 4 that is formed in the other end of the supporting part 2 and can detachably retain the electric cables 200.