To divide a decorative panel, mounted on the bottom opening part of a case body, into a panel frame body and a decorative frame, to securely suspend a case body in a low position according to a space in a ceiling; and simultaneously to correct a warp and deformation, occurring during molding of the panel frame body and the decorative frame, during suspension and fixing.

A protrusion part 4b protruded from an arm 4a of a decorative frame 4 positioned opposite to a side 1b of a panel frame body 1a is brought into contact with the side 1b of the panel frame body 1a to correct a warp and deformation occurring during molding of the panel frame body 1a or the decorative frame 4. Further, when a case body 1 is securely suspended in a case there is a surplus for a space in a ceiling, the decorative frame 4 is mounted by moving it to a position where it is positioned approximately flush with the panel frame body 1a having a suction grill. When the case body is securely suspended in a case there is no surplus for a space in a ceiling, the decorative frame 4 is mounted by moving it to a position above the panel frame body 1a having the suction grill.