A metal cap is provided with an RFID tag that includes a metal cap including a cylindrical main body part, a top plate part formed at one end of the cylindrical main body part, and an opening part formed at the other end of the cylindrical main body part, and an RFID tag disposed on the metal cap. The RFID tag includes an RFIC element disposed in the metal cap, and a loop antenna connected to the RFIC element. At least a portion of a loop opening of the loop antenna extends in a circumferential direction R of the metal cap while being exposed from an opening edge of the opening part of the metal cap to the outside of the metal cap.