To provide a heat treatment apparatus for waste plastics which is excellent in transferring molten waste plastics containing fine foreign substances and is capable not only of effective heating and dechlorination but also of improving crushability of the waste plastics solidified after the heat treatment.

The heat treatment apparatus for waste plastics is an improved one of an apparatus comprised of a vessel, which has a side wall having a jacket heated by passing a heating medium for receiving and keeping waste plastics in a molten state, a piping for circulating molten waste plastics by withdrawing it from a discharge valve attached to the bottom of the vessel and re-charging it from the upper part of the vessel, a measure for cleaning exhaust gas withdrawn from the upper part of the vessel and a measure for supplying above mentioned heating medium. Namely, an inner-rotational gear pump for transferring molten plastics and a heat exchanger for heating up molten waste plastics to be transferred are installed between the above mentioned discharge valve of the above mentioned circulation piping and the upper part of the above mentioned vessel.