Abstract: A mobile working machine for treatment of a ballast bed or subgrade for a ack comprised of rails fastened to ties includes a machine frame which is defined by a longitudinal axis and supported by undercarriages for movement in an operating direction along a track, and a track lifting unit which is vertically adjustably mounted to the machine frame between two undercarriages for lifting the track. The track lifting unit includes a load-bearing member which extends perpendicular to the longitudinal axis of the machine frame and has a length exceeding a tie length. The load-bearing member forms with its drives a structural unit, which encircles the track in a direction transversely to the machine frame during operation and is solely supported by the machine frame, and has a rolling element which is rotatable about an axis transverse to the longitudinal axis of the machine frame for providing a support for the ties of the track.