PURPOSE: To discover the bridging and blow by in a blast furnace in an early period with good accuracy and to make stable operation of the furnace by attaching plural pieces of heat resistant lance having optical fibers, etc., for observation of the furnace interior in the stage of operating the blast furnace to the shaft part of the furnace and directly monitoring the descending condition of the charged raw materials by the signals obtd. therefrom.

CONSTITUTION: Plural pieces of the heat resistant lances 2 mounted with the optical fibers, etc., having an objective lens system are installed to the shaft part 1A of the blast furnace 1. The signals for the furnace interior in the shaft part from the optical fibers of the heat resistant lances 2 are photoelectrically converted by a photoelectric converter 4 and are inputted to an image signal device 5 for monitoring and an image storage device 6 for data processing. The video signal from the device 5 is outputted to a monitor device 7, by which the signal is monitored and the moving picture image in the furnace is observed. The video signal from the device 6 is inputted to an analog- to-digital converter 8 to an image data processor 9, by which the data is processed. The result is fed via a digital to analog converter 10 to a blast rate controller 11 which controls the blast rate from tuyeres. The generation of the bridging and blow by in the blast furnace are thus suppressed and the blast furnace is stably operated.