A mobile pump device , in particular for use on mobile transport means , such as semitrailers, tank trailers, tank semitrailers , tankers and lorries , with a drive motor and with a rotary piston pump , wherein the drive motor comprises a motor shaft for driving the rotary piston pump and a motor housing , wherein the rotary piston pump comprises a housing with a pump housing part and a gear housing part , wherein two openings are formed on the pump housing part , one of which serves as a pump inlet and the other as a pump outlet , and wherein the rotary piston pump comprises at least two rotor units disposed rotatably in a pump chamber in the pump housing part , in order to convey a fluid from the pump inlet to the pump outlet , wherein the two rotor units are disposed on rotatably mounted rotor shafts , wherein each rotor shaft is equipped with a rotor gear arranged outside the pump chamber , wherein a drive pinion of a drive shaft of the rotary piston pump is coupled with one of the rotor gears , wherein the rotor gears and the drive pinion are accommodated in the gear housing part , characterised in that the motor shaft of the drive motor comprises a cutout at the front end , in which the drive shaft of the rotary piston pump is received and coupled with the drive shaft , and that the drive motor is connected via a connection flange with a U-shaped cross-section to the housing , wherein the connection flange forms the rear closure cover of the housing and at the same time the front closure cover of the motor housing , wherein the connection flange comprises two flanges running in parallel and spaced apart from one another, which form a surrounding "U" opened outwards. with a drive motor and with a rotary piston pump , wherein the drive motor comprises a motor shaft for driving the rotary piston pump and a motor housing , wherein the rotary piston pump comprises a housing with a pump housing part and a gear housing part , wherein two openings are formed on the pump housing part , one of which serves as a pump inlet and the other as a pump outlet , and wherein the rotary piston pump comprises at least two rotor units disposed rotatably in a pump chamber in the pump housing part , in order to convey a fluid from the pump inlet to the pump outlet , wherein the two rotor units are disposed on rotatably mounted rotor shafts , wherein each rotor shaft is equipped with a rotor gear arranged outside the pump chamber , wherein a drive pinion of a drive shaft of the rotary piston pump is coupled with one of the rotor gears , wherein the rotor gears and the drive pinion are accommodated in the gear housing part , characterised in that the motor shaft of the drive motor comprises a cutout at the front end , in which the drive shaft of the rotary piston pump is received and coupled with the drive shaft , and that the drive motor is connected via a connection flange with a U-shaped cross-section to the housing , wherein the connection flange forms the rear closure cover of the housing and at the same time the front closure cover of the motor housing , wherein the connection flange comprises two flanges running in parallel and spaced apart from one another, which form a surrounding "U" opened outwards. <EOS>