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)； determine a value of a control parameter (φ 1) corresponding to the first increase in transmembrane pressure； compare the value of the control parameter (φ 1) with a reference value (φ ref) and, if the value of the control parameter (φ 1) is greater than the reference value (φ ref), govern the regulatory device by imposing in the transmembrane pressure a second increase (δTMP2) that is greater than the first increase (δTMP1) in order to reach a third value of the transmembrane pressure (TMP3), wherein the setting sequence comprises a step of ending the sequence of setting and imposing the second pressure value (TMP2) as the setting value of the trans
