To provide a furnace pressure control system capable of controlling the furnace pressure in an opening part even if the pressure measurement in the opening part is difficult.

In this control system, a gas generation quantity acquiring means 92 acquires a gas generation quantity Qf in a furnace by measurement or calculation, and a set pressure determination means 94 determines a set pressure P1SV for setting a pressure PA in an input port to a desired value on the basis of the gas generation quantity Qf, and controls the furnace pressure so that a detected pressure P1 is matched to the set pressure P1SV. Accordingly, since the set pressure P1SV in the detecting position for setting the static pressure PA in the input port to zero can be determined on the basis of the gas generation quantity Qf having a fixed relation to the furnace pressure on the input port inside or the static pressure PA in a steady state, the static pressure PA in the input port can be controlled to zero regardless of the difficulty of furnace pressure measurement in the input port.