PURPOSE: To prevent an entrance frame body and a casing from snaking and to remove the possibility of leakage.

CONSTITUTION: The lower end part of an entrance frame body 2 is attached to the peripheral edge part 11 of an equipment unit floor part 1, and the cylindrical part 24 of the entrance frame body 2 is inserted into the open part 31 of a partition wall 3. A spacer 32 is inserted between the inner periphery of the open part 31 of the partition wall 3 and the cylindrical part 24 of the entrance frame body 2. The short cylindrical part 41 of a casing 4 abutted on the edge of the open part 31 of the partition wall 3 is inserted inside the cylindrical part 24 of the entrance frame body 2 to fix the short cylindrical part 41 of the casing 4 and the cylindrical part 24 of the entrance frame body 2 to the open part 31 of the partition wall 3.