PURPOSE: To prevent the overdrying of a humidity-controlled coal by estimating the decrease in loading of coking coal fed into a drier and/or the period wherein the humidity-controlled coal discharged from the drier becomes overdried and increasing the water content by adding water according to the estimate with a water-addition control apparatus.

CONSTITUTION: A water-contg. coking coal 2 is fed from a coal vessel 24 through a supply feeder 25, a conveyor 17, an entry chute 18, and a screw feeder 16 into a drier 1. A carrier gas is introduced through an air duct 21 into the drier 1; water vapor from the coking coal 2 is discharged through an exhaust duct 22; an exhaust gas cleaned with a dust collector 9 is exhausted; and the drain is recovered in a drain tank 23. A humidity-controlled coal 3 dried in the dryer 1 and having a water content of about 6% is discharged from an exit screw feeder 19. A humidity-controlled coal 3 having a water content of 5% or lower and discharged only for an estimated overdrying period estimated by a process calculator 8 is sprayed with water at the exit side of the dryer 1 using a water-addition control apparatus 32 comprising an industrial water supply system and a chemical supply system, this increasing the water content of and preventing the overdrying of the coal 3.