Pre-shredded, solid plastic and/or rubber waste is fed in to a melting unit (4), of two sequentially linked melting units (41,42), where the first melting unit (41) is constructed with an extruder axis (39) with a thread interruption (44), which shall cause solidity of the melted feedstock and formation of a compaction and a plug, thereby forcing the gases and steams to escape from the feedstock and to prevent back-flow of gases, via an interconnecting pipeline (28) a second melting unit (42) is mounted, from where the heated high pressure melted feedstock flows into the thermocatalytic reactor (7), where thermal decomposition of the hydrocarbon polymers in the feedstock takes place, then is followed by the collection and storage of the liquid product oil and gaseous end products.