A radial piston hydraulic pump or motor comprising a rotary cylinder block receiving a number of radial pistons whose outer ends are connected to bearing pads engaging the inner surface of an annular cam ring, the pads being rectangular in end view and located in an axial direction between inwardly facing shoulders of a surrounding casing, while the rotary cylinder block is free to move axially on a central supporting shaft and is located axially through the pistons and bearing pads.