An air-conditioning device for a vehicle seat has a seat, an air conditioning duct, a floor-side connection part, a seat-side connection part, and a connection duct. A position of the seat is adjusted in a front-rear direction. The air conditioning duct guides air, which is supplied from an interior air-conditioning unit, to a lower side of the seat. The floor-side connection part is provided in a vehicle-compartment floor on the lower side of the seat and connects to a downstream side of the air conditioning duct in an air flow direction. The seat-side connection part is provided in a seat bottom surface. The connection duct has one end portion connecting to the floor-side connection part and an other end portion connecting to the seat-side connection part. The seat-side connection part transfers across the floor-side connection part in the front-rear direction when a position of the seat is adjusted in the front-rear direction. The connection duct is deformable and stretchable. The floor-side connection part and the seat-side connection part are arranged at different positions in a left-right direction when viewed from a front side of a vehicle.