A supply heat quantity estimating method includes: estimating a change in carried-out sensible heat by in-furnace passing gas and a change in carried-in sensible heat supplied by a raw material preheated by the in-furnace passing gas, and estimating a quantity of heat supplied to the pig iron in a blast furnace in consideration of the estimated changes in the carried-out sensible heat and carried-in sensible heat. The estimating includes: estimating the carried-out sensible heat in consideration of the quantity of heat released to an outside, and estimating the change in the carried-in sensible heat in consideration of a change in a surface height of the raw material; and estimating a quantity of heat held in a deadman coke, and estimating the quantity of heat supplied to the pig iron in the blast furnace in consideration of the estimated quantity of heat held in the deadman coke.