Abstract: A pipe joint construction comprises a main pipe having a circular section of outer diameter D and one or more branch pipes having a circular section of outer diameter d. The wall thickness To of the main pipe is increased at the interior of the main pipe to a value T at the portion to which branch pipes are welded. The angle .phi. subtended by the portion of increased thickness at the center of the main pipe is determined by the following relationship, that is,1>.phi./2.pi..gtoreq.(.alpha..sup.2 /k)(d/D).sup.1/4 (D/T).sup.1/2 (T/To)where .alpha. represents a rigidity ratio and k is a constant.