To provide a technique for reducing and melting plastics, by which rubber and plastics are softened, melted or liquefied safely in or short time and also steam amount is proportionated to temperature and the plasticized plastics is liquefied.

Incombustible gas is heated at high temperature by a heat source and the current of the gas is made to collide with the plastics. Steam is generated by relating atomization amount to the measured value of temperature or by directly heating by the heat source. The plastics is introduced into a good heat conductive vessel and liquefied by the current of hot air containing steam of 250-450°C.