To provide a manufacturing method of a pipe having a knot part, by which two plates as preliminary formed bodies can be handled in a unit, the two plates are positioned to each other by overlapping and joining each first plate part of the two plates in a pre-stage of forming the preliminary formed bodies, positioning which has been necessary in a conventional information of joining two D-shaped tubes is unnecessary, and the joining strength of the knot part can be improved by overlapping and joining each first plate part of the two plates.

This manufacturing method comprises a first step S1 of overlapping and joining the two plates comprising the first plate part forming the knot part and a second plate part forming an outer circumferential part of a pipe with each other, a second step S2 of bending the second plate part so as to be symmetric to the first plate part and have a D-shaped section to form the formed bodies, a third step S3 of joining one end side of the first plate part of the formed bodies with an end part of the second plate part to form the preliminary formed bodies, and a fourth step S4 of forming the other end side of the first plate part as an outer curved side, and bending the preliminary formed bodies in the direction in which the length of both D-shaped parts is equal to each other.