PURPOSE: To attain to save dust collecting water of a dust collector collecting a converter waste gas by a method wherein a dust amount of the waste gas in the upstream side of the dust collector is measured and a dust collecting water amount determined by the relation of said measured valve and a preliminarily prepared dust amount and a dust collecting water amount is supplied.

CONSTITUTION: To the opening of a converter 1, a hood 2 having a skirt 2a mounted to the lower end part thereof is arranged so as to be closely contacted therewith and top blowing of oxygen is carried out by a lance 3 pierced through said hood 2. The hood 2 is communicated with a radiation part 4 and a waste gas passing therethrough is stored in a gas holder 9 through a primary dust collector 11 and a secondary dust collector 12 and discharged from a chimney 10 by operating a three-way valve 7 and a bypass valve 8 or the like. A dust amount is measured by a dust monitor 13 in the vicinity of a safety valve 4a and the measured value is sent to a flow amount operating and measuring apparatus 14 and a flow amount set signal is sent to control meters 11d, 12d to control opening degrees of the flow amount control valves 11b, 12b of water supply pipes 11a 12a to carry out to conserve a dust collecting water.