Device for the treatment of blood in operation with a single needle, with means (6) for transporting blood in an extracorporeal blood circuit with means (11) for collecting blood, in which the extracorporeal blood circuit has a tube of blood inlet (8) leading to an inlet (4A) of a blood treatment unit (2) and a blood return tube (9) that starts from an outlet (4B) of the unit for the treatment of blood and the means for collecting blood include a closed volume, means (8) for accumulating gas, which include a closed volume, a first joining route (21) to join the closed volume of the means (11) to collect blood with the closed volume of the means (18) to accumulate gas, such that in an arterial phase, when filling the means to collect blood from the means to collect blood, the gas displaced by the blood is transferred to the means to accumulate gas, containing the first route of junction (21) means (22) to interrupt the union, a means to compress (20) gas contained in a second junction route (19) to join the closed volume of the means (18) to accumulate gas with the closed volume of the means (11) for collecting blood, such that in a venous phase to empty the means for collecting blood in the means for accumulating gas, the accumulated gas is conducted with the means for compressing gas to the means for collecting blood, thereby the extracorporeal blood circuit is carried in the arterial blood phase and in the venous phase blood is drawn from the extracorporeal blood circuit.Dispositivo para el tratamiento de la sangre en funcionamiento con una sola aguja, con medios (6) para transportar sangre en un circuito extracorpóreo de la sangre con medios (11) para recoger sangre, en el que el circuito extracorpóreo de la sangre presenta un tubo de entrada de la sangre (8) que conduce a una entrada (4A) de una unidad para el tratamiento de la sangre (2) y un tubo de retorno de la sangre (9) que parte de una salida (4B) de la unidad para el tratamiento de la sangre y los medios
