PURPOSE: To permit air to be supplied only towards the seat which a driver takes from an air conditioner by installing a mechanism which operates as an opening and closing valve, integrally onto the bottom part of a seat cushion, in an air blowing-off port shielding apparatus for a ventilation seat of a car.

CONSTITUTION: A pressing plate 15 is laid between the side frames of a seat cushion 30 and fixed, and the both edge parts of a squeezing member 19 bent in U-figure shape are allowed to penetrate through the pressing plate 15 and projected upwardly and engaged with a cushion spring 18, and an elastic tube 13 is supported between the pressing plate 15 and the squeezing member 19. If the seat is vacant, the squeezing member 19 is pulled-up by the force of the cushion spring 18, and the elastic tube 13 is pressed onto the pressing plate 15 and collapsed flatly. Therefore, supply of air from an air conditioner is intercepted, and air is not blown-off from an air blowing-off port 14. When a driver takes the seat, the spring 18 bents, and the squeezing member 19 lowers, so the tube 13 pressed onto the pressing plate 15 is released, an communication between the ducts 12 and 14a is permitted, and air is blown-off from the air blowing-off port 14.