To provide both a method and an apparatus for a decomposition treatment of an organochlorine compound, solving a problem of a conventional decomposition treatment apparatus, recycling an alkali-methanol solution after a reaction, mixing the recycled solution with a new treating reagent, efficiently carrying out an operation so as not to cause a waste liquid and a drain after the reaction and decreasing a running cost.

This method for the decomposition treatment of the organochlorine compound comprises mixing the organochlorine compound with an alkali-methanol solution of the treating reagent, feeding the mixed solution to a pressure reaction process, heating and carrying out a reaction treatment, then separating the reaction product into carbon monoxide, a hydrogen gas, sodium formate and sodium carbonate of crystal precipitates and the reagent for use by a slurry separator 22, subjecting the separated reagent for use with anhydrous sodium sulfate and recycling the reagent for use as the treating reagent. The apparatus for the decomposition treatment of the organochlorine compound is equipped with a preheater 11 for mixing the organochlorine compound from a tank with the alkali-methanol solution from a treating reagent tank 3 and preheating the mixed solution to be treated, a reactor 20 for reacting the solution to be treated, preheated from the preheater through a piping, under pressure while heating and a cooler 25 for cooling the treatment solution reacted by the reactor, a dehydrating tank 31 for dehydrating with anhydrous sodium sulfate and a piping for recycling the dehydrated alkali-methanol solution to the treating reagent tank.