PURPOSE: To provide the laser knife having high cutting quality by forming the relatively wide part at the front end of a laser knife chip heatable.

CONSTITUTION: This laser knife consists of the laser knife chip 3 which is a transmission body for a laser beam and an optical fiber 1 for making the laser beam incident on the laser knife chip 3 and executes incision, etc., of viable tissues by converting the laser beam radiated from the optical fiber 1 to thermal energy in the laser knife chip 3 and heating the laser knife chip 3. The laser knife chip 3 has a blind hole 3a to be inserted with the front end of the optical fiber 1 and at least the inside wall 3b at the front end of th,e blind hole 3a is formed as a rough surface. Then, the relatively wide part of the outside surface of the laser knife chip 3 is heated, by which the entire region in contact with the viable tissues is almost uniformly heated.