PURPOSE: To ensure high efficiency for executing a work, and lower an economical burden.

CONSTITUTION: A leader 1 is constituted of inner space 10 faced to an exterior wall 30, and interior space formed outside the space 10 in such a way as freely opened and closed via a hinge 11, or gutter space 15. Coolant piping 28 is laid in the space 10, and this inner space 10 is secured to the exterior wall 30 with nails 12 driven from the outside through such a back plate 10 as fitted in contact with the exterior wall 30. In addition, a longitudinal piping slot 10B is drilled through the plate 10A for leading the piping 28 from an indoor unit. Also, the gutter space 15 is connectable to the side of an eaves gutter, so as to be opened and closed. The piping 28 is housed in the space 10 and, therefore, a work therefor can be executed simply by installing the leader 1, and efficiency for the work execution can be improved.