The invention relates to a truck-mounted concrete pump comprising a vehicle (12) and a concrete spreading boom (16) which is disposed on the vehicle (12) and includes a plurality of boom arms (22) that can be stowed, in the form of an arm assembly (24), on a vehicle-mounted boom supporting unit (14), and a boom hydraulic system which is designed to stow and unfold the arm assembly (24) and which includes a hydraulic cylinder (30) that moves the arm assembly (24) towards the boom supporting unit (14) in a stowing movement. In order to limit the boom stowing force, a protective circuit (20) which is coupled to the hydraulic cylinder (30) and automatically ends the stowing movement comprises a switching unit (32) that can be actuated under the load of the arm assembly (24).