A door operator for operating a door includes a housing, an output shaft with a cam disc, an opening piston guided in the housing, which piston, on a first side, bears against the cam disc, an energy accumulator acting upon the opening piston for storing a closing energy for the door, and a damping piston guided in a cylindrically shaped hollow space of a cylinder element, and which piston, on a second side, bears against the cam disc, wherein the cylinder element is firmly connected to the opening piston.