A paint mist collecting device for collecting a mist of paint particles produced when a paint is sprayed onto a workpiece within a paint booth includes a tubular duct having one end adapted to be connected to an outlet of the paint booth from which air containing the paint mist and a cleaning air are allowed to flow out, and a swirl-generating guide fin unit disposed inside the tubular duct and configured to force axial flows of the paint-mist-containing air and the cleaning liquid into a rotational movement to thereby generate a helical vortex as the paint-mist-containing air and the cleaning liquid flow downward along the tubular duct.