To provide a cutter capable of surely and efficiently cutting entire periphery of a mountain part at the prescribed place of a corrugate tube made of synthetic resin elliptic in cross section obtained by coating a pipe with synthetic resin.

A cutter main body 1 is provided with an insertion port 5 and an accepting hole 4 and provided with inserting grooves 6a and 6c for guiding the mountain part of the corrugate tube to a center part between opposed tip faces at this port 5 and the inner peripheral surface of the hole 4. Cutter plates 7 with first cutting blades 8 projecting from the center of the tip parts of the grooves 6a provided on the port 5 and second cutting blades projecting from the center of the tip parts of the grooves 6c provided on the side of the hole 4 are mounted to the right and left sides of the main body 1 in the state of being exchangeable. The corrugate tube is inserted to the portion 5 to cut the mountain parts of both side wall parts of the tube and then the main body 1 is rotated around the corrugate tube by 90° to continuously cut off the mountain parts of both tip curved wall parts of the tube by the blade 8 of one cutter plate 7 and the blade 9 of the other cutter plate.