PURPOSE: To secure an artificial muscle that is excellent in a reproduction of subtle motion and its universality by fitting a small diametral cylinder in a large diametral cylinder free of sliding motion in a pistonlike manner, and expanding or contracting this small cylinder to the large one in use of attraction and repulsion of magnetic force to be produced out of an electromagnet.

CONSTITUTION: A small diametral body inner part 2 is fitted in a large diametral body outer part 1 formed into cylindrical form each as free of sliding motion so as to make it retractable in a pistonlike manner. In addition, each permanent magnet (electromagnet) 4 is installed on respective opposed one ends of the body outer part 1 and the body inner part 2. Now then, each permanent magnet 4 is energized with current via respective power cords 3, whereby a magnetic field is generated there. In succession, an energizing direction of the electric current is selected, and thereby the body inner part 2 is expanded or contracted to the body outer part 1 in use of attraction and repulsion in a magnetic field, through which a muscular motion is produced. Moreover, some material with elasticity such as silicone rubber, by way of example, is used each in the body outer part 1 and the body inner part 2, whereby such a motion as approximate to a yet more natural muscle is produced in this way.