PURPOSE: To complete a cutting work safely in a shorter time without need for removal of earth by providing cutter revolving while pressed against the inner surface of a steel pipe while spinning.

CONSTITUTION: Upon starting of a motor 4, a rotating shaft 6 runs to rotate the body 15 of the cutter as reduced. As a hand pump 9 is operated to feed an pressure oil to a ram via a hose 12C, the cutter 29 and the motion roller strongly presses the inner surface of a steel pipe 20. The cutter 29 revolutes while spinning along the inner surface and cuts the wall of the pipe from inside. To cut the steel pipe 20, the peripheral speed thereof 29 is selected at nearly 50mm/sec. A pointer of a pressure gauge 11 lowers as soon as the pipe wall is broken through, which enables the detection of the finish in cutting. Releasing a valve of the hand pump 9 makes the cutter contract.