PURPOSE: To render the supply of collection material smooth, and prevent each part from being broken by setting a wall thickness head portion for housing a seal at the end of a collection pipe, and forming an annular chain bar between the collection pipe and the repairing inner hole.

CONSTITUTION: A wall thickness head portion 33 is provided at the end of a collection pipe 26, and each outer diameter of other portions is made smaller than the inner diameter of a hammer piston 17 and the inner diameter of a collection inner hole 23, and also an annular chain bar 35 is formed between the collector pipe 26 and the collection inner hole 23. Furthermore, a seal 34 for the collection pipe 26 and collection inner hole 23 is furnished not at an annular groove of the collection inner wall but at the wall thickness head portion 33 of the collection pipe 26. In this manner, through a drawing effect of the annular chain bar 35, a high pressure peak generated in the inner portion of the collection inner hole 23 is diminished, so that the seal 34 is prevented from being broken or spring out, and a quantity of supply of a collection material can be added to by raising its static pressure.