PURPOSE: To uniformly distribute the dispersion of power density at the time of defocus radiation within a defocus radiation range and to execute rapid and uniform burning of a diseased part by rotatably fitting a radiation optical fiber.

CONSTITUTION: An optical fiber for leading laser beams is divided into a light guiding optical fiber 11 and a radiation optical fiber 20 and the fiber 20 is rotatably fitted with the inclination of a prescribed angle from the optical axis. Thereby, the laser beams transmitted through the fiber 11 are made incident on the fiber 20 and the position with the highest power density can be uniformly distributed into the whole area of the radiation range at the time of defocusing by rotating the fiber 20. Since the fiber 20 with the prescribed angle from the optical axis is rotated, the peripheral diseased part 10 of a recessed part can be irradiated by the laser beams.