PURPOSE: To eliminate a useless idle running distance by arranging a control means for variably controlling a feeding speed of a robot hand on the basis of a signal from a distance sensor.

CONSTITUTION: After a robot is moved to a boring start position, it is checked whether an ultrasonic sensor 11 outputs a Lo signal or not. If a Lo signal is not detected, machining by a hole saw is started, and it is moved toward work at the predetermined approaching speed (approximately 10 times of a machining speed), and this movement is continued until a Hi signal is outputted from the ultrasonic sensor 11. If the Bi signal is outputted, the machining speed is reduced to the predetermined speed on the basis of a feeding speed instructing voltage from a feeding speed control unit 16 which variably controls a feeding speed of a robot hand 1, and then, cutting is carried out by means of the hole saw 10.