PROBLEM TO BE SOLVED: To provide a laser treatment instrument capable of guiding a plurality of fluids, a laser transmission path insertable through the laser treatment instrument, and an external tube that forms the laser transmission path.SOLUTION: The external tube 80 forms the laser transmission path 70 together with a hollow waveguide path 90 formed in long hollow shape to guide treatment laser light 57a, and permits the hollow waveguide path 90 to be inserted through an internal insertion space 81. In the external tube 80, a plurality of sub-passages 84 and cooling water passages 85 extending along the longitudinal direction of the insertion space 81 are provided on the outside of the hollow waveguide path 90 inserted through the insertion space 81.
