A control changeover system in a blast furnace system including a septum valve having a capability of controlling the furnace top pressure in the blast furnace system and a blast furnace gas energy recovery turbine also having a capability of controlling the top pressure by front pressure control is operated with a slight difference between preset values of the top pressure set by a top pressure setter respectively for control by the septum valve and control by the turbine, whereby the predominance in controlling the top pressure between the two control capabilities is automatically changed over from one capability to the other in accordance with an operation of varying the turbine load by means of a load setter provided for the turbine while the two control capabilities are maintained in operative state.