A pulverized coal-fired boiler efficiently supplies air to a central part of a furnace and the neighborhood of a furnace wall, thereby promoting mixture with combustion gas, and reducing both NOx and CO.The main after air ports are structured so as to jet air having a large momentum for enabling arrival at the central part of the furnace, and the sub-after air ports are structured so as to jet air having a small momentum to the neighborhood of the wall face of the furnace, and a sectional center of each of the sub-after air ports is within a range from 1 to 5 times of a caliber of the main after air ports from a sectional center of each of the main after air ports.