A dust-collecting apparatus of a vacuum cleaner includes a first dust-collecting unit, a second dust-collecting unit, and a dust receptacle. The second dust-collecting unit is adapted to be mounted to one side of the first dust-collecting unit. The dust receptacle is adapted to be mounted on a lower part of both the first and the second dust-collecting units, and the dust receptacle is adapted to store dust separated by the first and the second dust-collecting units. The first and second dust-collecting units are arranged so that air discharged from the first dust-collecting unit enters the second dust-collecting unit.