Abstract: In extrusion processing in which diameter reduction is performed by pressing a raw pipe having a core bar inserted therein into a die having a small inner diameter portion on its tip end side, a differential thickness pipe having a thick-walled portion at its tip end can be molded using a core bar having a small cross-section portion formed at its tip end. It is also possible to mold a differential thickness pipe having a thick-walled part at an intermediate axial position by using a raw pipe having a thin-walled portion at its tip end. For example, such a raw pipe can be molded by extrusion processing using a core bar having no small cross section portion at its tip end, prior to the above-described formation of the thick-walled portion. When higher dimensional accuracy is required, a so-called “counter punch” may be used in the formation of the thick-walled portion.