To eliminate the risk of members getting loose even in case of being rotated normally and reversely and connect and detach the members easily without using a special jig at the time of replacing parts in a down-the-hole hammer of such constitution that a top sub connected to a joint adaptor is connected to the upper end of a piston case with a built-in piston and that a drive sub enclosing a hammer bit movably forward/backward is connected to the lower end of the piston case.

A joint adaptor 18 and a top sub 17 are formed as an integral member. A piston case 1 and the top sub 17, and the piston case 1 and a drive subs 5 are respectively connected by forming connection parts on the side of the top sub 17 and drive sub 5 into polygonal shafts 19 or spline shafts while forming connection parts on the piston 1 side into recessed parts 20 into which the polygonal shafts 19 or spline shafts are fitted, and fitting both connection parts to each other. Pinholes 21 are formed at fit-in boundary parts, across both connection parts, and a pin 22 to be a key is inserted in a retractable state into each pinhole 21.