To obtain a piping joint having a flat O-ring mounting place and free from parting line and to omit a cutting process for eliminating the parting line.

An annular member 32 concentrically circular to a screw core 31 is integrally formed at the upper end of the screw core 31 incorporated in a split mold 33 and the inner surface of the annular member 32 is formed into a stepped shape and a screw is formed to the small diameter part 32a of the member 32 and a flat circumferential surface is formed to the large diameter part 32b of the member 32. After molding, when the screw core 31 is revolved to be pulled out, a place wherein an O-ring is mounted corresponds to the large diameter part 32b to become a flat circumferential surface free from a parting line.