To provide an air cushion mat, which is properly weighty in use, comfortably fit to a buttock in use on a seat, and scarcely shifted and maintained in the previous seating condition when a user sits on the mat again after leave it, so as to secure a stable seating condition.

An air cushion mat is provided with a breathable auxiliary mat 8, an airtight air bag 3 having an openable plug 2 in an air port, and a cushion cover 5 having a port 4 provided with a fastener which can be opened according to the openable plug 2 position. The air bag 3 is inserted beneath the auxiliary mat 8 inside the cushion cover 5. When the openable plug 2 of the air bag 3 is closed after it is opened for lowering a pressure, the compressed surface shape of the air bag 3 can be maintained for a fixed time at least by an action of a breathable cushion member 6 inserted inside the air bag 3.