PURPOSE: To automatically adjust a chuck jaw moving by a fastening ring during boring by providing a means that the rotation of an adjusting ring disengaging a lock member of the fastening ring is restricted by a stopper in a drill chuck of shock boring.

CONSTITUTION: A chuck jaw 5 forming a hole drilling tool receive part 4 is moved by a fastening ring 8 guided rotatably by a chuck body 1 connectable with a hole drilling spindle. Moreover, as for a locking device of the fastening ring 8, a locking member 10 is engaged with a locking clearance 9 by a locking spring 11. Furthermore, the locking member 10 escapes from the locking clearance 9 due to the rotation of an adjusting ring 15. In this case, the rotation of the adjusting ring 15 is restricted by a stopper 16. Moreover, an inertia ring 17 in which the locking member 10 is arranged is energized in the same direction as the fastening ring 8 when a chuck is closed by an adjusting spring 19. Furthermore, the rotation of the inertia ring 17 is restricted to a size of d rotary path in the fastening ring 8.