An object is to provide a laser treatment tool capable of guiding a plurality of fluids, a laser transmission path insertable into such a laser treatment tool, and an external tube for forming the laser transmission path. In an external tube 80 which forms a laser transmission path 70 together with a lengthy hollow waveguide path 90 for guiding treatment laser light 57a and has an inner insertion space 81 for allowing insertion of the hollow waveguide path 90, a plurality of sub passages 84 and cooling water passages 85 are provided outside the hollow waveguide path 90, inserted into the insertion space 81, along a longitudinal direction of the insertion space 81.