A process for the thermal degradation of polymer, which comprises feeding the polymer to an extruder for melting, transferring the molten polymer at a constant rate to a tubular thermal degradation reactor through a constant rate transferring means connected to the extruder, and thermally degrading the polymer in the reactor. This process allows a low-molecular polymer with a high quality to be produced continuously with a simple apparatus in a simple step. Particularly it is possible to obtain a high-quality thermal degradation wax with a good hue and a reduced content of foreign matter continuously in a stabilized manner for a long period of time by thermally degrading an olefinic polymer in a simple apparatus and efficiently removing the formed volatile component from the reaction mixture.
