To provide an air mat device which is not too hard and is comfortable to sleep on and which is provided with a high dehumidifying effect by blowing air.

An external shape constitution member consisting of a cushion core 10 and a cushion pad 11 provided with ventilation holes 20 on a side face is formed of chemical fiber cotton, and a blowing bag 15 is fitted in its inner space with a base air bag 12. Slit-like blowing holes 16, which are never opened by pressure higher than a fixed value, are formed at the bag 15 to discharge air from an inner space through the holes 16.