In the present invention, a blocking tube (11) has a tubular blocking layer (11a) made of a material having barrier properties, and a tubular covering layer (11b) which is disposed in contact with at least the inner peripheral surface of the blocking layer (11a) and is made of a material of the same quality as a base resin. One end portion of the covering layer (11b) protrudes further toward the outside than an end portion of the blocking layer (11a) which is disposed on the outer periphery side. In the blocking tube (11), the inner peripheral surface of the covering layer (11b) forms the inner surface of a pouring hole (5), and the end face on the one end portion side in an axial direction of the covering layer (11b) and the outer peripheral surface of the covering layer (11b), which protrudes from an end portion in the axial direction of the blocking layer (11a) are embedded in the base resin in contact with the base resin.