Original Text (This is the original text for your reference.)

PURPOSE: To provide a method of productively manufacturing a synthetic resin pipe with spiral inner surface ribs or grooves and an extrusion mold used for the manufacture without causing any deformation such as distortion or the like after piping and adversely affecting the spiral ribs so that they are reduced in size by hot drain or the like flowing therein, and further without impairing the drainage capacity semipermanently.