The invention relates to a mobile work machine, particularly a concrete pump truck. The work machine comprises a chassis (10) that has at least four wheels (11) that belong to a wheel axle, in pairs. Furthermore, at least two support legs (20) disposed laterally on the chassis, in pairs, are provided, which legs have a telescope segment configured as an extension tube (28) articulated onto the chassis (10), and a foot part (24) that can be extended downward, in telescope-like manner, and supported on the ground, preferably by hydraulic means. In order to guarantee simple handling of the support mechanism, it is proposed, according to the invention, that the extension tube (28) of the support legs (20) is configured in the manner of a two-arm lever, forming a lower lever arm (40), with reference to the pivot axis (34), which contains the foot part (24), and an upper lever arm (42), preferably spring-supported in the pivoting-out direction.