To provide a waste plastics pyrolyzer designed to respond to the change in the condition of the waste plastics therein as their pyrolysis proceeds, diminish the add-on of carbonized matter onto the inside of the pyrolyzer and accomplish efficient thermal conduction to the waste plastics.

This waste plastics pyrolyzer has such a scheme that a hollow cylinder 2 with an inner diameter of R (m) is installed and designed to revolve at a rate of N (rpm) about the central axis thereof by a relevant mechanism 21, waste plastics 3 are fed by a relevant mechanism 22 into the hollow cylinder 2 which is charged with spherical or cylindrical solids 1 for agitation with a weight of M (kg), and the inside of the hollow cylinder 2 is heated by a relevant mechanism 25 to ≥250°C; wherein the relationship: N×R/M≥5 is met.