Hydrostatic radial piston unit of the cam-lobe type of construction comprising: - a non-rotary, stationary casing comprising a through hole defining a rotational axis of the hydrostatic radial piston unit; - a cylindrical, rotary casing mounted rotary to the non-rotary, stationary casing in an axial overlapping area in which a front end portion of the non-rotary casing and a rear end portion of the rotary casing overlap such that the rotary casing can rotate relatively to the stationary casing around the rotational axis; - a park brake mechanism comprising at least two brake discs arranged adjoined in the overlapping area, wherein one brake disc is rotationally fixed to the non-rotary casing and the other brake disc is rotationally fixed to the rotary casing; - an end cover closing the non-rotary casing on a rear end side of the hydrostatic radial piston unit facing away from the rotary casing, wherein the end cover pre-tensions a disc spring against a disc-shaped brake piston both located in the rear end portion of the stationary casing to generate an axially oriented spring force, characterized in that - a stationary shaft is arranged coaxially with the rotational axis in an internal cavity formed by the stationary casing, the rotary casing, the end cover and a front cover, wherein a cylinder block housed non-rotary in the front end portion of the rotary casing is in torque-proof connection with the stationary shaft, - the rotary casing comprises an internal cam-lobe surface, against which working pistons accommodated in the cylinder block can act; - the axially oriented spring force can be forwarded by the brake piston to at least one brake pin arranged in an axially oriented bore in the stationary casing, in order to press the brake discs against each other when the brake piston on the face opposite to the disc spring is not forced to move towards the end cover. - a non-rotary, stationary casing comprising a through hole defining a rotational axis of the hydrostatic radial piston unit; - a cylindrical, rotary casing mounted rotary to the non-rotary, stationary casing in an axial overlapping area in which a front end portion of the non-rotary casing and a rear end portion of the rotary casing overlap such that the rotary casing can rotate relatively to the stationary casing around the rotational axis; - a park brake mechanism comprising at least two brake discs arranged adjoined in the overlapping area, wherein one brake disc is rotationally fixed to the non-rotary casing and the other brake disc is rotationally fixed to the rotary casing; - an end cover closing the non-rotary casing on a rear end side of the hydrostatic radial piston unit facing away from the rotary casing, wherein the end cover pre-tensions a disc spring against a disc-shaped brake piston both located in the rear end portion of the stationary casing to generate an axially oriented spring force, - a stationary shaft is arranged coaxially with the rotational axis in an internal cavity formed by the stationary casing, the rotary casing, the end cover and a front cover, wherein a cylinder block housed non-rotary in the front end portion of the rotary casing is in torque-proof connection with the stationary shaft, - the rotary casing comprises an internal cam-lobe surface, against which working pistons accommodated in the cylinder block can act; - the axially oriented spring force can be forwarded by the brake piston to at least one brake pin arranged in an axially oriented bore in the stationary casing, in order to press the brake discs against each other when the brake piston on the face opposite to the disc spring is not forced to move towards the end cover.