PURPOSE: To always maintain a lance in a sound state by feeding a cooling gas from a separately provided cooling gas piping for cooling the lance to the lance when the supply of a carrier gas to the lance of which the top end is projected into a blow pipe is interrupted.

CONSTITUTION: High-temp. air for blasting is blown through the blow pipe 15 into a blast furnace 17 through a tuyere 16. The lance 1 attached to the pipe 15 is connected to a transport piping 2 having an on-off valve 8 and the cooling gas piping 7 having a check valve 6 and an on-off valve 7 in this case. The valve 8 is therefore closed immediately when the supply of the cooling gas of the piping 2 stops. On the other hand, the valve 7 of the cooling gas line is opened to supply the cooling gas (for example, air) to the lance 1. Accidents of the blow-off of the high-temp. gas from the inside of the furnace owing to damage of the lance and the downtime of the blast furnace for the purpose of exchanging the damaged lance are thus eliminated and life of the lance is extended.