PURPOSE: To fit a diffuser by simple work according to requirement, for making a ceiling interior not to be seen through an exhaust port.

CONSTITUTION: Sections set directly above the exhaust port concealing pieces 7 of the connecting horizontal-piece section 3 of a cradling A are provided with exhaust ports 8, and a ceiling interior is contrived not to be seen through the exhaust ports 8. End sections in the same directions as the longitudinal directions of the T-bar sections 1 of the exhaust ports 8 on both sides are brought close to each other. The section of the connecting horizontal-section 3 between both the exhaust ports 8 near each other is set to be cut off. The section which can be cut off is cut off, and on this space, a diffuser can be fitted.