Provided is an optical fiber for producing heat wherein a reflection tube (13) is wrapped on its outer peripheral surface by a heat conduction tube (14) to block laser beam from being irradiated outside, and a plurality of grooves are formed on a side of an optical fiber (11) so as to transmit laser beam to the side of the optical fiber (11) at 360° around a central axis of the optical fiber (11) where a cloth (12) is peeled away such that the area where heat is produced is expanded to a whole length direction of the optical fiber (11) where the cloth (12) is peeled away between the optical fiber (11) and the reflection tube (13).
