In drying coal to be used as fuel for a coal-fired boiler, the coal is dried at a temperature of 80 to 150° C. by using combustion exhaust gas having passed through an air heater for the coal-fired boiler. Moreover, after medium-quality or low-quality coal is heated to a temperature of 300 to 500° C. at a heating rate of not less than 100° C. per minute and then cooled to a temperature of 250° C. or below at a cooling rate of not less than 50° C. per minute, the resulting reformed coal is cooled to a temperature of 70° C. or below and stored for 1 month or more in a state of isolation from the atmosphere. In producing the aforesaid reformed coal, the medium-quality or low-quality coal is heated by using combustion exhaust gas obtained at the outlet of an economizer included in the coal-fired boiler equipment or at the outlet of a denitrator included therein.