To facilitate occupant's seating on or getting out of a seat supported with an air spring even at the time of driving an engine.

This vehicular seat suspension device retains a seat 1 at a preset seat position by disposing an air spring 8 between the floor surface F and the seat 1 of a vehicle, and regulating air pressure through air switching valves 14, 16, and is provided with, especially, an engine key 30 for ON-OFF switching an engine; a side brake switch 31 for detecting the operating condition of a parking brake; a door switch 32 for detecting the opening condition of a door 3 formed against the seat; and a controller 18 which switches the air pressure switching valves 14, 16 for air supply or exhaust. When the engine key 30 is OFF or the pulled-up condition of a parking brake lever and the opened condition of a door 3 are detected under ON condition of the engine key 30, the controller 18 switches the air pressure switching valves 14, 16 to exhaust side to lower the seat 1.