The invention relates to a mobile work device, particularly a mobile concrete pump. The work device comprises essentially a chassis (12), two front and two rear support booms (38, 40) that can be moved out from a transport position into at least one working position relative to the chassis (12) and have a support leg (42) that can be supported on a substratum, in each instance, raising the chassis, as well as a drive unit (47) for controlling work assemblies and/or the support booms. A particular feature of the invention consists in that at least one of the support booms (40) having a beam profile or hollow-chamber profile has a transverse perforation (48) that can be configured as a housing for an ancillary assembly (52) of the drive unit, for example.