PURPOSE: To utilize the attracting force of a permanent magnet which can smoothly and certainly slide a slide plate owing to the few number of parts and accurate assembly dimensions.

CONSTITUTION: A female locking piece B having a slide plate 5 to slidingly contact-in the hole edge of an inserting hole 8 on the underside of the engaging jaw part 9 on the projection 2 of a male locking piece A which is attracted and moved with the permanent magnet of the male locking piece A is composed of the first plate 3 with rising side plates 3a on sides, the second plate 4, and the slide plate 5 slidably assembled between the first and second plates. A part for joining the first and second plates 3, 4 is provided with a recessed notch part 10 and a protruding piece 11 entering the part 10, and the first and plates 3, 4 are weldedly fixed with the protruding piece 11 and the recessed notch part 10 kept in a mutually engaged state.