A pen needle for coupling to a pen-type syringe for injecting medication into a user and preventing re-use thereof, the pen needle comprising: a needle for delivering medication; a needle hub provided with a needle fixing body, into which the needle is inserted, at a center of the needle hub; a small cap having a ring-shaped small cap upper surface including a small cap upper surface through-hole, and a small cap cylindrical wall body connected to the small cap upper surface, the small cap covering the needle and the needle protruding outside the small cap through the small cap upper surface through-hole when the small cap upper surface is pressed against the skin of the user; a spring mounted around the needle fixing body for providing an elastic restoring force to the small cap; a wing-type support unit provided with a needle fixing body insertion tube having a cylindrical shape, and having a plurality of wing-type support wings disposed along a rim of the needle fixing body insertion tube; characterized by a medium cap provided at an outer side of the small cap cylindrical wall body, mounted over the hub lower body, and having a ring-shaped medium cap upper surface that is connected to a medium cap cylindrical wall body; wherein when the small cap is moved downward inside the medium cap due to a pressing pressure generated by contact between the small cap and the skin of a user, the same pressing pressure is delivered to the wing-type support unit upper wing in contact with the small cap upper surface so that the wing-type support unit accommodated inside the small cap is also moved downward with the small cap inside the medium cap, whereby the needle N protrudes from an upper end of the small cap to the outside thereof by a length corresponding to the downward movement of the small cap inside the medium cap, and pierces the skin of the user by the length of the needle which protrudes outside so that the user may administer an injection medication, wherein a protrusion or bump of the needle fixing body is inserted into a supporting rod and a wing-type support unit recess so that the wing-type support unit moved downward with the small cap is fixed to and engaged with the needle fixing body, and, after the user administers the injection medication, the small cap is moved upward inside the medium cap due to an elastic restoring force of the spring to return to an original position thereof while the wing-type support unit is not moved upward with the small cap, and the wing-type support unit upper wing supports an inner side surface of a wing-type support unit blocking bump formed at a bottom of a lower portion of the small cap that is moved upward such that the small cap that moved downward once is prevented from being moved downward again to prevent reuse of the needle N. a needle for delivering medication; a needle hub provided with a needle fixing body, into which the needle is inserted, at a center of the needle hub; a small cap having a ring-shaped small cap upper surface including a small cap upper surface through-hole, and a small cap cylindrical wall body connected to the small cap upper surface, the small cap covering the needle and the needle protruding outside the small cap through the small cap upper surface through-hole when the small cap upper surface is pressed against the skin of the user; a spring mounted around the needle fixing body for providing an elastic restoring force to the small cap; a wing-type support unit provided with a needle fixing body insertion tube having a cylindrical shape, and having a plurality of wing-type support wings disposed along a rim of the needle fixing body insertion tube; characterized by a medium cap provided at an outer side of the small cap cylindrical wall body, mounted over the hub lower body, and having a ring-shaped medium cap upper surface that is connected to a medium cap cylindrical wall body; wherein when the small cap is moved downward inside the medium cap due to a pressing pressure generated by contact between the small cap and the skin of a user, the same pressing pressure is delivered to the wing-type support unit upper wing in contact with the small cap upper surface so that the wing-type support unit accommodated inside the small cap is also moved downward with the small cap inside the medium cap, whereby the needle N protrudes from an upper end of the small cap to the outside thereof by a length corresponding to the downward movement of the small cap inside the medium cap, and pierces the skin of the user by the length of the needle which protrudes outside so that the user may administer an injection medication, wherein a protrusion or bump of the needle fixing body is inserted into a supporting rod and a wing-type support unit recess so that the wing-type support unit moved downward with the small cap is fixed to and engaged with the needle fixing body, and, after the user administers the injection medication, the small cap is moved upward inside the medium cap due to an elastic restoring force of the spring to return to an original position thereof while the wing-type support unit is not moved upward with the small cap, and the wing-type support unit upper wing supports an inner side surface of a wing-type support unit blocking bump formed at a bottom of a lower portion of the small cap that is moved upward such that the small cap that moved downward once is prevented from being moved downward again to prevent reuse of the needle N.