A device for establishing venous inflow to a blood reservoir of an extracorporeal blood circulation system including a venous inflow line from a patient to the blood reservoir and an arterial outflow line extending from the blood reservoir to the patient, the device comprising: a restricting unit configured for clamping the venous inflow line in order to act on the venous inflow amount to the blood reservoir in the range below a basic value, the basic value comprising a value established by gravitational conveyance while the inflow line is not restricted by the restricting unit; a vacuum unit configured for applying a vacuum to the blood reservoir in order to act on the venous inflow amount to the blood reservoir in the range above the basic value; a control device that includes a single operating element having a plurality of operating positions and configured to be manipulated in a single manipulation by a user to establish both a degree of closure of the venous inflow line and an amount of vacuum in the blood reservoir for venous inflow to the blood reservoir at, above or below the basic value; and a venous flow sensor disposed on the venous inflow line and configured to measure a venous flow rate of the circulating blood in the venous inflow line and to send a venous flow rate signal representing the venous flow rate to the control device; wherein, at each operating position of the plurality of operating positions, the control device is configured to supply a different combination of a restricting unit setting that corresponds to an extent of a restriction of the venous inflow amount to the blood reservoir below the basic value, based on the manipulation of the single operating element in the single manipulation and a vacuum unit setting that corresponds to the operating position to the vacuum unit for establishing the amount of vacuum in the blood reservoir to define an extent of the increase in the venous inflow amount to the blood reservoir above the basic value based on the manipulation of the single operating element in the single manipulation, without the use of a blood level sensor and blood level signals; wherein the control device is configured to automatically determine a flow rate adjustment value based on the venous flow rate measured by the venous flow sensor and the selected operating position; wherein the control device is configured to automatically send a first flow rate adjustment signal to the restricting unit and a second flow rate adjustment signal to the vacuum unit such that the restricting unit adjusts the degree of closure at the venous inflow line and the vacuum unit adjusts the amount of vacuum in the blood reservoir to collectively adjust the venous flow rate of the circulating blood in the venous inflow line by the flow rate adjustment value. a restricting unit configured for clamping the venous inflow line in order to act on the venous inflow amount to the blood reservoir in the range below a basic value, the basic value comprising a value established by gravitational conveyance while the inflow line is not restricted by the restricting unit; a vacuum unit configured for applying a vacuum to the blood reservoir in order to act on the venous inflow amount to the blood reservoir in the range above the basic value; a control device that includes a single operating element having a plurality of operating positions and configured to be manipulated in a single manipulation by a user to establish both a degree of closure of the venous inflow line and an amount of vacuum in the blood reservoir for venous inflow to the blood reservoir at, above or below the basic value; and a venous flow sensor disposed on the venous inflow line and configured to measure a venous flow rate of the circulating blood in the venous inflow line and to send a venous flow rate signal representing the venous flow rate to the control device; wherein, at each operating position of the plurality of operating positions, the control device is configured to supply a different combination of a restricting unit setting that corresponds to an extent of a restriction of the venous inflow amount to the blood reservoir below the basic value, based on the manipulation of the single operating element in the single manipulation and a vacuum unit setting that corresponds to the operating position to the vacuum unit for establishing the amount of vacuum in the blood reservoir to define an extent of the increase in the venous inflow amount to the blood reservoir above the basic value based on the manipulation of the single operating element in the single manipulation, without the use of a blood level sensor and blood level signals; wherein the control device is configured to automatically determine a flow rate adjustment value based on the venous flow rate measured by the venous flow sensor and the selected operating position; wherein the control device is configured to automatically send a first flow rate adjustment signal to the restricting unit and a second flow rate adjustment signal to the vacuum unit such that the restricting unit adjusts the degree of closure at the venous inflow line and the vacuum unit adjusts the amount of vacuum in the blood reservoir to collectively adjust the venous flow rate of the circulating blood in the venous inflow line by the flow rate adjustment value.