A fluid such as water or a mixture of water and gas flows through the space between the guard tube 5 and the sheath tube 10 to detour around the ball lens 9 through a passage of a holding member as explained in FIG. 4B, and flows through the space between the laser probe 1 and the sheathing metal pipe 8 to be emitted on the diseased part on the basis of irradiation of a laser light.