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