PURPOSE: To enhance the aesthetic appearance by downwardly projecting a whole surface of a ceiling excepting the peripheral part thereof, and by forming ventilation holes on one side surface of the projected part facing a wall panel.

CONSTITUTION: The ceiling 2 of a unit bath 1 is composed of a shallow and wide pan-like ceiling panel 20 and a frame-like auxiliary panel 21 surrounding therearound, and a recess part 9 projecting downward is formed. A plurality of ventilation holes 3 are formed at one side surface 22 at a corner of the recess part 9. An ventilation box 10 is provided at the corner including the ventilation holes 3 on the inside of the recess part 9, and is connected to a duct, a ventilation fan and the like for forced ventilation. With this arrangement, it is possible to enhance the aesthetic appearance of the ceiling surface without the necessity of a projected ventilation grill for covering the ventilation holes.