A buckle device that includes a buckle with which a tongue supported by a seat belt becomes engaged, and a buckle-moving device which moves the buckle between a storage position at which the buckle is stored when the buckle is not used and a use position at which the buckle is retained in a used state in which the seat belt is fastened, wherein the buckle-moving device is adapted to move the buckle between the storage position and the use position with a rotational movement, and wherein the buckle device further comprises a buckle-supporting member that is adapted to support the buckle and includes an external-force-reducing mechanism which reduces an external force applied to the buckle-supporting member if the external force is larger than a predetermined force, wherein the external-force-reducing mechanism is a buckle-moving device that allows the buckle to move in a fore-and-aft direction of a vehicle when the external force is applied to at least one of the buckle and the buckle supporting member in the fore-and-aft direction of the vehicle. The buckle may be hidden in the vehicle seat at the storage position. The buckle does not obstruct the occupant when the occupant sits on or gets off the vehicle seat, and the occupant can smoothly sit on or get off the vehicle seat.