A cannula needle or catheter needle (1) comprises a first portion (2) provided with a catheter (4) to be introduced into a vein and a second portion (3) provided with a cannula (5) which is inserted into the catheter (4) on introducing this latter into the vein, but is separable to be withdrawn from it after this introduction has taken place, the cannula (5) provided with a point (13) being associated with its own support (10) and being arranged to cooperate with a hollow (at 17) protection element (15) through which said cannula (5) is inserted and within which it is locked when said cannula (5) is separated from the catheter (4). The protection element (15) is coupled to the first portion (2) and is interposed between this and the second portion (3). Said protection element (15) is separable from the first portion (2) during the withdrawal of the cannula (5) from the catheter (4), said cannula (5) comprising coupling means (65) for its locking to said element (15) which are arranged to cooperate with the inner part (19A) of the cavity (17) of this latter in which the cannula (5) moves during said withdrawal and when the point (13) of the cannula (5) is totally inserted into said cavity (17). This cooperation, together with the movement of the cannula (5), causes the protection element (15) to become detached from said first portion (2) of the cannula needle (1), the protection element (15) comprising a part (44) for closing the cavity (17) in which the cannula (5) is disposed in the closed position on detaching the protection element (15) from the first portion (2) of the cannula needle (1).
