PURPOSE: To move a travel body in a stable posture by providing a pair of rollers rotating in contact with the guide section of a guide rail.

CONSTITUTION: The mounting section 12 of a cylinder tube 2 is loosely coupled to a mounting groove 6 on the upper surface of a guide rail 1, and the cylinder tube 2 is mounted on the guide rail 1 in such state as capable of being slightly afloat along a plane approximately orthogonal with a lengthwise direction. Also, a fixing guide roller 25 is fitted to the body 20 of a travel body 4 movable along the external surface of the cylinder tube 2 at one side, and an adjusting guide roller 26 is fitted to the body 20 at the other side. In this case, the rollers 25 and 26 are kept in freely rotatable contact with guide members 9 laid on both sides of the guide rail 1. Also, a magnet coupling is fitted so as to be faced to a piston 3 movable in the cylinder tube 2 and the travel body 4. According to this construction, the travel body 4 reciprocates synchronously with the piston 3, thereby stabilizing the moving posture of the travel body 4 at the time of carrying an article.