PURPOSE: To eliminate fear of magnetic interference and surely prevent lateral displacement of male unit by engaging the edge collar of a hole reaching the hole bored to a ferromagnetic plate on the pole surface with the hole edge and forming an abutting edge collar by raising a case on the circumference of the pole surface against which the ferromagnetic plate abuts.

CONSTITUTION: A ferromagnetic plate 2 is mounted to the one pole surface of a magnet 1 while a ferromagnetic plate 7 having a hole reaching the hole 1a is mounted to the other pole surface, the magnet 1 is held at the center of case 6 with the hole edge at the plate 7 formed as the folded engaging edge collar 7a for the inside of magnet hole 1a, and the plate 7 is fixed onto the surface of magnet 1 with the raised edge collar 6a of the case 6. A male unit to be engaged with a female unit is composed of a ferromagnetic plate 3, a ferromagnetic bar 5 protruded from the plate 3 and a fitting metal 9 having bending leg pieces 9a and prevents lateral displacement thereof as a stop device through engagement between the edge collar 6a and circumference of plate 3. A magnetic path on the pole surface is focused to the plates 2, 7 when the male unit is removed therefrom or engaged therewith and the line of magnetic force of plate 2 passes the bars 4 and 5 and also passes between edges of aperture at the inside of plate 7.