Apparatus for extracorporeal blood treatment, comprising: at least one treatment unit (2) having at least a first chamber (3) and at least a second chamber (4) that are separated from each other by a semipermeable membrane (5)； at least one blood collection line (6) connected to an inlet port of the first chamber (3) and prepared to draw blood from a patient； at least one line (7) of return of the blood connected to an exit port of the first chamber and prepared to return the treated blood to the patient； at least one infusion line (9； 9a, 9b) of a replacement fluid； at least one fluid evacuation line (10) connected to an outlet port of the second chamber in order to receive at least one fluid that has been filtered through the semipermeable membrane (5)； a device (20) regulating a transmembrane pressure between the first chamber and the second chamber of the treatment unit, the regulating device being active in at least one of the lines； and a control unit (15) connected to the regulating device (20) and configured in such a way that it executes a sequence of setting the transmembrane pressure, the sequence of setting comprising the following steps: governing the regulating device imposing a first increment ( δTMP1) at a first transmembrane pressure (TMP1) value in order to reach a second transmembrane pressure (TMP2)； determining a value of a control parameter (δ1) corresponding to the first increase in transmembrane pressure, in which the control parameter comprises a parameter selected from a group comprising: - a variation between the replacement flow in the line of infusion (9； 9a, 9b) in the first transmembrane pressure value (TMP1) and the replacement flow in the infusion line in the second transmembrane pressure (TMP2)； - a variation between the ultrafiltration flow (QUF) through the membrane (5) in the first transmembrane pressure value (TMP1) and the ultrafiltration flow in the second transmembrane pressure value (TMP2)； compare the value of the control p
