PURPOSE: To miniaturize a drill and, at the same time, to promote boring capacity.

CONSTITUTION: A drilling bit 4 is provided to the front end of a casing 1, a piston 7 capable of reciprocating motion is housed in the casing and, at the same time, a valve body 12 having a plurality of ports 13a, 13b and 13c are arranged between the piston and the circumference of the casing 1 so that they are capable of reciprocating motion. A supply channel 16 supplying pressure oil and a discharge channel 17 discharging oil are formed in specific positions of the casing. The piston and valve body are reciprocated by supplying pressure oil to a chamber constituted of the casing, piston and valve body, percussion force is given to the bit with the advance of the piston and, at the same time, turning effort is given to the bit through a chuck with the backward movement of the piston.