PURPOSE: To cut a pipe without applying an external force onto the pipe by securing the synchronous transfer of a cutting machine and the pipe, maintaining the state for detecting the top edge of the pipe by a top-edge detecting mechanism.

CONSTITUTION: The top edge of a pipe 1 which advances rightward is detected by a top-edge detecting mechanism 3, and a traveling driving means 12 starts operation at the same time. Said top-edge detecting mechanism 3 feedback- controls the traveling driving means 12 so that the speed for maintaining the state for detecting the top edge of the pipe 1 can be obtained. A cutting machine 2 and the top-edge detecting mechanism 3 connected with the cutting machine 2 through a steel pipe 4 are allowed to travel on the rail 6 of a rack 5 by the traveling driving means 12. Therefore, the synchronous transfer of the cutting machine 2 and the pipe 1 is secured. Therefore, the pipe 1 is not applied with the axial compression force due to the cutting machine 2, and bending, deformation of covering resin, and breakage are not generated, and the automatic cutting to a constant dimension is permitted.