To install a tool holder to a plate member by either linear move or curvature move.

The plate members 27 and 28 are installed on a chain 24, and fork-shaped positioning piece parts 27b and 28b (only one part is illustrated for each) are formed on them. In both outer side surfaces of the tool holder 26, groove parts 38b and 39b to be inserted and engaged with the positioning piece parts 27b and 28b of the plate members 27 and 28 are formed. Width of the groove parts 38b and 39b is set wider at an insertion starting end part of the positioning piece parts 27 and 28, gradually narrowed toward the insertion terminating end side, and roughly similar to plate thickness of the positioning piece part at the insertion terminating end part. The groove parts 38b and 39b of the tool holder 26 can be engaged with the positioning piece parts 27b and 28b of the plate parts 27 and 28 by either linear move or curvature (arc- shaped) move. An engagement state is locked by a lock device 30.