To certainly fix a movable body on a middle part of a wire without costing labor.
An engaging member 232 to engage a wire installation member 231 is provided on a middle part of a wire 64. A hole 235 to be engaged the engaging member 232 fixed on the middle part of the wire 64 is formed roughly in the center of an upper groove part 233 formed on an upper surface of the wire installation member 231. Additionally, wire insertion holes 236, 237 free to insert the wires 64 on both sides of the engaging member 232 through them are formed on both sides of a hole 234 to be engaged. The wire insertion holes 236, 237 are formed by extending in a direction orthogonal with the travelling direction of the wire 64. The wire installation member 231 is fixed on the wire 64 by respectively inserting both end parts of the wire 64 into the wire insertion holes 236, 237 from above the upper groove part 233 and fitting the engaging member 232 fixed on the wire 64 in the hole 235 to be engaged.