To ensure secure and easy maintenance for body inside, etc., by connecting a drain pipe with a drain pan having a drain hole at a lowermost part of a body in the shape where the connection coincides a lower surface opening of the body, and demountably holding an inspection hole cover on the drain pan through protective means.

A drain pan 13 is provided in the form coincident with an opening 2 in a lower surface of a body 10 to a lowermost part of which a drain pipe 11 is connected and which has a drain hole 12, and on a lower surface of which pan 13 a mounting tool holding part is disposed. A mounting tool 15 hooked on and engaged with the mounting tool holding part 14 is mounted on an inspection hole cover 18 disposed to close an inspection hole 17 formed in a ceiling surface 16. The inspection hole cover 18 is demountably provided through protection means composed of the mounting tool holding part 14 and the mounting tool 15. Hereby, maintenance for the inside of the body, etc., is facilitated.