A limestone supply device is provided for supplying calcium carbonate to an upstream of a desulfurization device and a heat exchanger disposed on an upstream of the desulfurization device on a flue gas duct through which flue gas discharged from a combustion engine in which a fuel burns flows. An air pollution control system having the limestone supply device is provided, including a calcium carbonate accumulate unit configured to accumulate calcium carbonate, a calcium carbonate transport unit configured to transport the calcium carbonate accumulated in the calcium carbonate accumulate unit, a calcium carbonate supply unit configured to supply the calcium carbonate transported by the calcium carbonate transport unit to the flue gas duct, and a moisture supply unit configured to supply moisture to a region to which the calcium carbonate is supplied by the calcium carbonate supply unit.