To cut a communication pipe line from its inside by providing a plurality of cutter means pressed to the slope of a tip expanded part by the forward movement of a piston and protruded in a perpendicular direction.

A piston 35 is formed to be conical in its front side, a cutter base 40 is disposed so as to be contacted with the slope 38 of this conical shape and a cutter blade 41 is driven by the cutter base 40. A pipe cutting device 20 is attached to the tip of a boring rod, the boring rod is moved to a specified cutting spot and, by starting a plunger pump so as to pressure-feeding water, the piston 35 is moved forward, the cutter blade 41 is protruded and in this position, a pipe is cut from its inside by the cutter blade 41.