Provided is a plastic waste solid fuel incinerator comprising: an incinerator housing which has, on the upper portion thereof, a gas outlet through which combustion gas is discharged; a fuel supply unit which transfers and supplies a plastic waste solid fuel; a first combustion unit which continuously transfers and burns the supplied plastic waste solid fuel; a first air supply unit which supplies air needed for combustion to the first combustion unit; a combustion gas induction unit which induces the combustion gas generated from the first combustion unit toward the lower portion of a first combustion chamber; a second combustion unit which is arranged in the lower portion of the first combustion unit and comprises a downward injection nozzle unit which downwardly injects the combustion gas supplied through the combustion gas induction unit in order to reburn the combustion gas; and a second air supply unit which is arranged in the lower portion of the second combustion unit and supplies the air needed for combustion to the second combustion unit by downwardly injecting the air. Accordingly, there is an advantage of allowing continuous combustion using combustion gas generated during the combustion of the plastic waste solid fuel without using a separate auxiliary fuel, thereby reducing incineration costs.