A pipe joint comprising: a flare joint body including a male screw part and a slope surface with reduced-diameter tip; a cap nut including a female screw part threadedly attached to the male screw part and provided at a base end of a hole part, and a housing space part with a constant diameter section, a stepped section, and a tapered section with reduced-diameter tip provided at an intermediate area of the hole part; and a stop ring fitted in the housing space part, including a base-end pressure-contacting slope surface contacting the slope surface with reduced-diameter tip under pressure, and having a tip provided with a plastically-deformable and substantially cylindrical thin part and a pipe extraction preventing tooth part formed at a tip head of the substantially cylindrical thin part, wherein the tooth part includes a back tooth and a front tooth arranged at a tiny interval (W 36), the back tooth has a trapezoidal or substantially trapezoidal sectional shape with a linear first tip side, and the front tooth has a trapezoidal or substantially trapezoidal sectional shape with a linear second tip side, as the cap nut threadedly moves forward, the first tip side of the back tooth and the second tip side of the front tooth of the stop ring come into a state of tightly contacting an outer peripheral surface of a straight tip part of a connection target pipe under pressure to generate pipe extraction resistance composed of extraction resistance generated by the back tooth and extraction resistance generated by the front tooth, wherein at the hole part of the cap nut, the tapered section with reduced-diameter tip is defined by a base-end steep slope tapered part and a tip gentle slope tapered part. a flare joint body including a male screw part and a slope surface with reduced-diameter tip; a cap nut including a female screw part threadedly attached to the male screw part and provided at a base end of a hole part, and a housing space part with a constant diameter section, a stepped section, and a tapered section with reduced-diameter tip provided at an intermediate area of the hole part; and a stop ring fitted in the housing space part, including a base-end pressure-contacting slope surface contacting the slope surface with reduced-diameter tip under pressure, and having a tip provided with a plastically-deformable and substantially cylindrical thin part and a pipe extraction preventing tooth part formed at a tip head of the substantially cylindrical thin part, wherein the tooth part includes a back tooth and a front tooth arranged at a tiny interval (W 36), the back tooth has a trapezoidal or substantially trapezoidal sectional shape with a linear first tip side, and the front tooth has a trapezoidal or substantially trapezoidal sectional shape with a linear second tip side, as the cap nut threadedly moves forward, the first tip side of the back tooth and the second tip side of the front tooth of the stop ring come into a state of tightly contacting an outer peripheral surface of a straight tip part of a connection target pipe under pressure to generate pipe extraction resistance composed of extraction resistance generated by the back tooth and extraction resistance generated by the front tooth, wherein at the hole part of the cap nut, the tapered section with reduced-diameter tip is defined by a base-end steep slope tapered part and a tip gentle slope tapered part.