PURPOSE: To make possible the adjustment of a direction for blowing the underfloor air at a small angle with a floor, enhance comfort and prevent tumble at the time of walking for increasing safety.

CONSTITUTION: An air supply apparatus 3 with a blower 2 laid in underfloor space S for blowing the underfloor air, is mounted on a floor lid 4 concealing an opening A on the floor body F of a house, and the lid 4 is provided with a port 6 communicated with the air outlet 5 of the apparatus 3. In addition, the port 6 is fitted with a freely rotatable cover body 9 in such a way as projected hemispherically from the lid 4 and having a blowout hole 7 for blowing the underfloor air at a small angle with a floor.