Device for pinching a flexible tube in a pinching region, comprising two cross-sections (3a, 3b), each having a hollow part (4a, 5a) with a male indentation and a female indentation, respectively, able to be either in the open state where they are separated from one another or in the closed state where they are drawn together and closed on one another by reciprocal-locking means (25a and 25b) and where the surfaces (13 and 14) of the indentations (11a and 11b) form a positive pinching passage of the tube, characterized by the fact that: - the cross-sections (3a and 3b) are contoured and extend along the longitudinal axis, with the positive pinching closing zone extending over a certain axial length, - in the transverse straight cross-section, the male indentation has a U shape with a core and two wings (38a and 38b); in the transverse straight cross-section, the female indentation has a U shape with a core and two wings (36a and 36b); and in the transverse straight cross-section, the pinching passage has a U shape with a core and two wings (42a and 42b), - the two wings (36a, 38a and 36b, 38b) opposite each pair of wings facing the male indentation and the female indentation will draw together toward their ends that are opposite to the cores of the indentations (35 and 37), at least in the zone of these ends, and each of the two wings (42a and 42b) of the pinching passage has, between the surfaces of the two indentations (11a and 11b), an opening whose width will diminish towards its end that is opposite to the core of the pinching passage, - the width of the opening of the pinching passage is at most slightly smaller than twice the thickness of the wall of the flexible tube to be pinched, - the pinching device is disposable and performs an operation of the tube closing on itself in the pinching region preventing any passage of fluid into the tube. - the cross-sections (3a and 3b) are contoured and extend along the longitudinal axis, with the positive pinching closing zone extending over a certain axial length, - in the transverse straight cross-section, the male indentation has a U shape with a core and two wings (38a and 38b); in the transverse straight cross-section, the female indentation has a U shape with a core and two wings (36a and 36b); and in the transverse straight cross-section, the pinching passage has a U shape with a core and two wings (42a and 42b), - the two wings (36a, 38a and 36b, 38b) opposite each pair of wings facing the male indentation and the female indentation will draw together toward their ends that are opposite to the cores of the indentations (35 and 37), at least in the zone of these ends, and each of the two wings (42a and 42b) of the pinching passage has, between the surfaces of the two indentations (11a and 11b), an opening whose width will diminish towards its end that is opposite to the core of the pinching passage, - the width of the opening of the pinching passage is at most slightly smaller than twice the thickness of the wall of the flexible tube to be pinched, - the pinching device is disposable and performs an operation of the tube closing on itself in the pinching region preventing any passage of fluid into the tube.