The invention relates to a mobile working machine, particularly an automatic concrete pump, having a chassis (10) designed as a tractor-trailer. The tractor-trailer comprises a tractor (12) and a multi-axle semi-trailer (14) supporting the working machine and connected to the tractor by means of a fifth wheel (16). A support construction (38) that can be supported on a surface (40) is located in the area of the semi-trailer (14). The support construction (38) comprises two front stabilizers (42′, 42′) and two rearward stabilizers (44), each pivotable between a transport position and at least one support position relative to the semi-trailer. Means for raising and securing the tractor (12) are further disposed on the semi-trailer (14), so that the tractor (12) forms a ballast weight for stabilizing the semi-trailer supported by the support construction (38) on the base (40) in the support position. According to the invention, the bearing points (48′, 48) of the front stabilizers (42′, 42′) comprise a hollow space (80) through the center of the axis, and the means for raising and securing the tractor disposed on the semi-trailer (14) each comprise a lift member (82) extending through the central hollow area (80) of the bearing point (48, 48) from top to bottom and releasably attachable to the tractor (12).