To provide a furnace inside pressure control method of a carbonaceous solid reducing agent filled vertical furnace for restraining a change in gas blowoff from an exhaust port even if a furnace inside melt is continuously discharged.

A powder and grain-like raw material is blown in a filling layer of a carbonaceous solid reducing agent via an upper stage tuyere or upper-lower stage tuyeres for blowing in high temperature air, and exhaust gas of the vertical furnace for melting and reducing the raw material is sucked by an exhauster, and when adjusting furnace inside pressure by changing a rotating speed of the exhauster, a detecting position of the furnace inside pressure is set lower than the height of the upper stage tuyere. In this case, an interval in a plan view between a detecting position of the furnace inside pressure and a tuyere position for blowing in the raw material is desirably set to 20 degrees or more in a furnace central angle.