<p>A main pipe (60) is lined using a pipe lining material (62) that blocks the opening (61b) of a lateral pipe (61) branching from the main pipe. An in-pipe work robot (1) is provided with a cutting nozzle (30) for spraying a pressurized fluid material or pressurized granular material onto the pipe lining material (62) of the main pipe (60). The cutting nozzle (30) is moved to a predetermined position inside the main pipe (60) and rotated about a vertical axis (22a) by a rotary mechanism (23, 28) to cut the lining material (62) between the first and second pipes (60, 61) by the pressurized fluid material or pressurized granular material sprayed from the cutting nozzle (30) in order to form an opening (61b) for communicating the main pipe (60) with the lateral pipe (61). The cutting nozzle (30) can be moved in desired positions to drill holes accurately without damaging the internal peripheral surface of the lateral pipe (61).</p>
