To solve a problem on practical application of an artificial muscle, an auxiliary device for care and rehabilitation without uncomfortable feeling is enabled if it shrinks well to obtain the strong strength and to be downsized, however, a conventional pneumatic artificial muscle has a low shrinkage rate and, when a covered fiber is widely expanded at the outer circumference, the tangled thread is slid and the mesh of the net is widened to form a weak section, then the pressure is focused on there, and the inner tube explodes, and the pressure-resistant gets troubled.

An artificial muscle is composed of a mesh fiber (braided lace) and a tube inside, the fiber structure is made of the strong braided lace whose knots are small and the fiber is not slid, the braided lace is covered on the outer circumference of the tube to make an expandable body, another braided lace as a shrinkable body with a smaller inner diameter than the outer circumference of the expandable body is covered on the outer circumference of the expandable body, and the expandable body is different from a rubber tube because it shrinks while pushes and expands the outer shrinkable body to provide over 30% of the shrinkage rate.