A facility for continuously manufacturing a galvanized steel sheet includes a continuous annealing furnace, a snout, and a galvanization bath. The furnace is divided into a heating zone, a soaking zone, and a cooling zone. The bath is directly connected to the furnace through the snout. The facility has a dewpoint meter and a spray port and a suction port for a furnace gas that are provided in at least one of the zones, gas cyclic paths which connect the spray port and the suction port to a refiner, and a dewpoint meter and a humidification device that are provided in the snout. The gas cyclic paths are separately formed for the respective connected zones. The refiner functions so that a measured value of the dewpoint meter is equal to a target dewpoint, and the humidification device functions so that a measured value of the dewpoint meter in the snout is equal to a target dewpoint for the snout.