A smoke control system of a building including a supply air duct installed in an interior of the building having a plurality of floors in a vertical direction, including a plurality of openings corresponding to the plurality of floors, respectively, and one end of which is exposed to an outside of the building, a blower that supplies air to the supply air duct, and a plurality of automatic differential pressure dampers installed in a plurality of ancillary rooms provided on the plurality of floors, respectively, to be adjacent to the plurality of openings. Opening areas of the plurality of openings increase as locations of the plurality of openings become farther away from a point, at which air is supplied to the supply air duct by the blower.