PROBLEM TO BE SOLVED: To recover and reutilize highly pure hydrocarbons without substantial need for pretreatment of the waste and without discharging environment-poluting substances by treating a crushed product of a plastic mixed waste, in which chlorinated resins are mixed, with a specifically concentrated aqueous sodium hydroxide solution.
SOLUTION: A crushed plastic mixed waste, in which chlorinated resins are mixed, and an aqueous sodium hydroxide solution having a concentration of 30-50 wt.% are accommodated in a reaction vessel in the state of the plastic mixed waste being immersed in the aqueous sodium hydroxide solution, and heated to 250-310°C to react the plastic mixed waste with the aqueous sodium hydroxide solution so that the waste is at least dechlorinated. The crushed plastic mixed waste preferably has a maximum length of 5-15 mm. The ratio of the plastic mixed waste to the aqueous sodium hydroxide solution is preferably 1-8 wt.%. The retention time in the reaction vessel is approximately 0.5-5 hrs.