To mount an air outlet by effectively providing a chamber at a suitable position even in the case of executing a ceiling by forgetting mounting of a hanging bolt for fixing the chamber at a slab.

Legs 11 opening so as to be installed on a ground are provided on a rear surface of a ceiling plate 51 to be disposed on a periphery of a second opening 7 for mounting a first opening 5 for mounting a duct 41 and an air outlet 51 in the case of executing at a chamber body 3 having the opening 7. The legs 11 are mounted rotatably at the body 3 substantially in an L shape so as to be opened in a radial direction. The legs 11 are installed on the ground at the rear surface of the plate 51 to support the body 3 to mount the outlet 61.