A dusting device for a cleaning machine, being capable of detachably assembled to a bottom of the cleaning machine, includes at least a first rotary disc, a second rotary disc, an idler pulley, a driving rope unit, and dusting elements respectively attached to the first and second rotary discs. The driving rope unit is movably disposed on the first rotary disc, the idler pulley, and the second rotary disc. The first rotary disc is driven to rotate by a motor installed in the cleaning machine, and the idle pulley is driven to rotate by the driving rope unit and the first rotary disc, so as to further drive the second rotary disc to rotate in conjunction with the first rotary disc, whereby enabling the dusting elements to rotate to dust and clean a surface to be cleaned.