PURPOSE: To provide a method for very easily adjusting the clearance of a sliding part in a mechanical structure.

CONSTITUTION: Magnets are mounted on any one of a fixed body 1 or a moving body 2 composing a sliding part in a mechanical structure. The magnetic force of the magnets acts on the direction in which the fixed body 1 and the moving body 2 are attracted each other. Thus, the magnetic force of the magnets is utilized as a pre-load for adjusting the clearance between the fixed body 1 and the moving body 2. The magnitude of the pre-load is adjusted by rotatably mounting a permanent magnet 4 and by rotating the permanent magnet to change the direction of magnetic poles NS, changing attraction by magnetic force or by mounting an electromagnet and by adjusting its supply current to change strength of magnetic force. Thus, the clearance of the sliding part is to be adjusted.