PURPOSE: To make an automatic replacement of worn throw away tip, by successively shifting a tip, successively pushed out from the magazine that contains an unused tip, to the tip feed out passage (rail).

CONSTITUTION: An unused tip A2 is housed in a magazine 10, and fed out toward a feed bar 24 by a push-out plate 14 actuated by a hydraulic cylinder 45. When moved the feed bar 24 to a backmost position with a worn tip A1 made coincident to a collector hole 69, the tip A2 is pushed out and the tip A1 is pushed toward the direction of a collector box 68. The tip A1, being shallowly engaged to the protruding substance supported by a piano wire, is disengaged if pushed by the tip A2, and made dropping down into the collector box 68. At the same time, the tip A2 comes to be engaged to the protruding substance, and used for the next cutting work.