A needle tip protector comprising: a protector main body having an insertion passage (108, 110) where a needle is inserted, the protector main body being mounted against the needle by means of having the needle inserted into the insertion passage (108, 110) such that the protector main body being movable in an axial direction of the needle while extending along the same direction; at least one flexible plate (100, 102) attached to the protector main body extending toward the needle tip at a location orthogonally away from the needle inserted into the insertion passage (108, 110) of the protector main body in a way that allows its distal end to undergo flexural deformation in a direction of getting closer to the needle; a protection part (130, 131) placed at the distal end of the flexible plate (100, 102) that protects the needle tip by being placed at a protective position to cover the needle tip when the flexible plate (100, 102) undergoes flexural deformation in the direction of having its distal end get closer to the needle in a state where the protector main body is moved toward the needle tip of the needle inserted into the insertion passage (108, 110); an action ring that is externally fitted about the protector main body in a movable way in the axial direction of the needle and makes the protection part (130, 131) placed in the protective position by causing flexural deformation of the distal end of the flexible plate (100, 102) in the direction of having its distal end get closer to the needle through an advance movement toward a distal end side of the protector main body; and a slip-stop mechanism (128, 142, 148) that prevents the action ring from slipping out of the protector main body in the axial direction of the needle, the needle tip protector being characterized in that the protector main body integrally comprises the at least one flexible plate (100, 102), with the advance movement of the action ring toward the distal end side of the protector main body, the action ring presses the at least one flexible plate (100, 102) toward the needle so that the at least one flexible plate (100, 102) undergoes flexural deformation in the direction of having its distal end getting closer to the needle, it is arranged that the flexural deformation of the at least one flexible plate (100, 102) in the direction of having its distal end getting closer to the needle is held when the protector main body has reached to the needle tip of the needle so as to avoid that the distal end of the at least one flexible plate (100, 102) contacts an outer periphery of the needle with an urging force, the slip-stop mechanism (128, 142, 148) includes: at least one anti-retraction tab provided on the protector main body in an elastically deformable way so as to extend toward the needle tip at a location orthogonally away from the axial direction of the needle inserted into the insertion passage (108, 110) of the protector main body, which allows the action ring to advance toward the distal end side of the protector main body by elastic deformation in the direction of getting closer to the needle, and when the protection part (130, 131) of the flexible plate (100, 102) is brought to the protective position by the action ring, prevents the action ring from moving back toward the proximal end side of the protector main body by means of restoring from the state of elastic deformation and contacting a rear-end surface of the action ring located on an opposite side of an advancing direction of the action ring; and at least one first engaging surface placed on the rear-end surface of the action ring that restricts elastic deformation of the anti-retraction tab in the direction of getting closer to the needle by engaging itself with the anti-retraction tab in contact with the rear-end surface, and wherein the at least one anti-retraction tab comprises two anti-retraction tabs that are provided on the protector main body so as to extend toward the needle tip in a state of being placed on both sides of the needle, whereas at least one first engaging surface comprises two first engaging surfaces that are each provided on the rear-end surface of the action ring being in contact with the two anti-retraction tabs.