To achieve power saving of a dust collector by quantitatively estimating the produced quantities of dust, calculating a rotational frequency of the dust collector on the basis of the estimated produced quantities of dust, operating the dust collector with the rotational frequency and eliminating overaction of the dust collector.

In a dust collecting method for collecting dust produced when raw materials are carried in a storage tank 2 by using a dust collector 4, the generated quantities of dust from the raw materials are estimated from the storage rage of the raw materials stored in the storage tank 2, the brand of the raw material and moisture content of the raw materials. A rotational frequency of the dust collector 4 is calculated on the basis of the estimated produced quantities of dust, and the dust collector 4 is operated so as to make the rotational frequency.