To prevent air leakage without using conventional engaging means between a duct connecting adaptor and a body frame.

In a duct connecting adaptor 27, a ventilator provides the lower end part of a main plate part 28 with the first mounting piece 30, and the lower end part of a side plate part 32 with the second mounting piece 33, so as to assign the first and second mounting pieces 30 and 33 to different 3 sides of a crate, when being mounted at the crate of the ceiling. When a body frame 36 is inserted into an opening part of the crate to be mounted, there is a composition in which the first and second mounting pieces 30 and 33 are pressed against the crate from the down part by a flanged portion 39. As a result of this, the tilt of the main plate part 28 to the side of a duct 35 can be prevented, thus preventing air leakage without using conventional engaging means between a duct connecting adaptor 27 and the body frame 36.