A needle safety blocker comprising a support piece (14, 15) of the needle protection cover； and a needle protection cover (16) comprising an elongated part (18) coupled to said support piece of the needle protection cover and slidable axially with respect to the support part of the needle protection cover , wherein the needle protection cover additionally comprises a cylindrical protection cover (20) having two open ends to contain at least a portion of the needle, wherein said elongated piece has a length greater than the length of said needle； and where, during use, the needle protection cover is axially slidable with respect to the needle from a first position in which the tip of said needle is discovered to a second position in which the tip of the needle is cover； characterized in that the needle security blocker comprises a locking means for selectively securing the needle protection cover in a first locking position that can be released and a second locking position that cannot be released； where the position of the needle protection cover either in the first or in the second locking position corresponds to the position of the needle protection cover in the second position, and； wherein the locking means comprises a projection (26) located in an element between the support piece of the needle protection cover and the elongated part； and a first and a second groove (28) in the other element between the support piece of the needle protection cover with the elongated part, so that the coupling between said projection and said grooves selectively prevents the axial movement of the needle protection cover when the needle protection cover is in said second position.Un bloqueador de seguridad para aguja que comprende una pieza (14, 15) de soporte de la cubierta de protección de aguja； y una cubierta (16) de protección de aguja que comprende una pieza (18) alargada acoplada a dicha pieza de soporte de la cubierta de protección de aguja y deslizable de manera axial co
