PURPOSE: To avoid a damage of engaging pieces due to a rotation of female and male clamping elements and an unexpected twisting force of the elements by forming the female element forming an engaging implement of a permanent magnet, opening a hole at the center, providing a ferromagnetic rod projected downwardly at the male element faced with the female element, and engaging the rod within the hole.

CONSTITUTION: A female clamping element is composed of a case 5 made of a nonmagnetic material, a permanent magnet 1 having an engaging hole 1a through its center is contained in the case 5, a ferromagnetic plate 2 is secured to the lower surface of the magnet, and the peripheral edge of the plate is secured with a bent part 5b of the case 5. Subsequently, a ferromagnetic rod 2a is projected into the hole 1a, a disc 4a is mounted on the lower portion of the plate 2, the peripheral edge of the disc is caulked with its edge 4b to be twisted, and a hole communicating with the hole 1a is opened on the upper surface of the case 5. A male clamping element is arranged corresponding to the female element thus formed, and a ferromagnetic rod 3a to be engaged with the hole 1a is provided on the lower surface of the plate 3 supported by a mounting washer 11a. In this manner, the engagement of the elements are rigidly performed.