Mobile work machine having a chassis that is designed as a tractor-trailer, a multi-axle tractor unit and a multi-axle semi-trailer that carries the work machine and is connected with the tractor unit by means of a fifth-wheel coupling, having a support construction that is disposed in the region of the semi-trailer and can be supported on a surface, raising the tractor-trailer, which construction has two front support booms disposed at bearing locations on the tractor unit end of the semi-trailer, symmetrical to the longitudinal chassis axis, which can be pivoted between a transport position and at least one support position, by means of a hydraulically driven activation mechanism, in each instance, and two rear support booms that can be pivoted between a transport position and at least one support position, whereby the semi-trailer has means for raising and holding the tractor unit in place.