TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The material injection process, thermal decomposition process, thermal shrinkage of residue and residue emission process are sequentially and continuously performed in a batch operation. The completion of thermal shrinkage of residue is determined when value measured by thermal shrinking temperature sensor installed in thermal decomposition apparatus attains a predetermined regulation value, and heating or thermal decomposition apparatus is terminated and subsequently the residue is emitted out. The residue exhaust valve is closed and residue emission process is stopped, when the temperature of emitted residue measured by the emission residue temperature sensor installed in the residue discharge portion is less than the predetermined regulation value. Subsequently, injection and thermal decomposition of plastic waste material of next batch process are carried out. The time (T1) required for completion of residue emission process is calculated by measuring the time for measured value of the emission residue temperature sensor to attain a value greater than the predetermined specified temperature. The accumulation time (T1) is compared with accumulation time (T0) of residue emission process of previous batch process. The heating temperature during thermal shrinkage process of next batch process is increased or reduced when the accumulation time (T0) is lesser than the accumulation time (T1) and accumulation time (T0) is greater than the accumulation time (T1), respectively. The time (T1) required for the measured value of the emission residue temperature sensor to attain a value more than the predetermined specified temperature, is integrated. The heating temperature of residue thermal shrinkage process of the next batch process is increased or decreased, when the integral value is lesser and greater than the integral value of the previous batch process, respectively. Alternately, the time (T1) is integrated and average value of each integral value of each batch process is calculated. The heating temperature of residue thermal shrinkage process of the next batch process is increased or decreased, when the integral value of batch process is lesser and greater than the calculated average value, respectively. The thermal shrinkage process is stopped when the measured value of the thermal shrinkage temperature sensor, which is an input value of the driving control apparatus, attains the predetermined regulation value. Preferred Apparatus: The emission residue temperature sensor is installed in the discharge side of the residue exhaust valve. The waste plastic processing apparatus further has an accumulation unit for measuring input value accumulation time or integrator for integrating the time required for the measured value of the emission residue temperature sensor to attain a value more than the predetermined specified temperature, optionally average value calculation unit for calculating average value of the integral values of each batch process, comparison unit for comparing the accumulation time with accumulation time of the previous emission process or for comparing the integral value with the integration time of the previous residue emission process or for comparing the integral value of each batch process with the calculated average value, and adjustment unit for adjusting the heating temperature of thermal shrinkage process based on the comparison by the comparison unit. The apparatus further has nozzle for blowing an inert gas to prevent deposition of residue in the emission residue temperature sensor.