PURPOSE: To improve seal performance by applying shot peening to at least one of metal to metal seal parts, and adjusting a surface roughness degree after the shot peening to the metal to metal seal parts, so as to reduce unevenness of a limit value of the seal performance.

CONSTITUTION: In a steel pipe joint 2 of containing 2% or less Cr by weight ratio and also having a metal to metal seal part 4, shot peening is applied to at least one of the metal to metal seal parts 4. Now when assumed x (μm) for surface mean roughness and y (μm) for maximum roughness after the shot peening of the metal to metal seal part 4, surface roughness is adjusted so as to satisfy a relation where 1.50≤x≤5.0, 10≤y≤30.