A needle tip protector (78) is configured in such a manner that a flexible plate (100, 102) is provided to a protector main body (92) over which an action ring (94) is mounted and that the flexible plate (100, 102) undergoes flexural deformation when the action ring (94) is moved to a predetermined position relative to the protector main body (92). When the flexible plate (100, 102) undergoes flexural deformation, a needle tip (18) of an inner needle (10) to which the protector main body (92) is mounted is protected by a protection part (130, 131) placed at a distal end of the flexible plate (100, 102). The needle tip protector (78) is also provided with a slip-stop mechanism (128, 142, 148) for preventing the action ring (94) from slipping out of the protector main body (92) in an axial direction of the needle (10).
