When a mechanism constituent unit having a base is secured to a magnetic base at a predetermined position, a fixture having a detachable mechanism inside itself is employed, and the fixture is disposed on a notch of the base of the mechanism constituent unit in a non-adsorption state in which magnetic force lines of a permanent magnet of the detachable mechanism permeate the fixture. In this state, a rotation casing is rotated 90 degrees to be in a lock state, and a fixing casing is firmly adsorbed to the magnetic base such that magnetic force of the permanent magnet inside it permeate to the magnetic base side. Thus, the mechanism constituent unit base is firmly sandwiched by a pressing portion of the fixing casing and the magnetic base, and the base of the mechanism constituent unit is firmly secured to the magnetic base at a predetermined position.