An apparatus and a method for treating an object material containing a heavy metal and a noxious organic halide, and a method of treating soil. The treating apparatus is provided with an air-tight door (115b) and a retort (115c) as interfaces for taking out to the outside a discharged gaseous material containing an evaporated material from an object material to be treated which is heated under vacuum in an air-tight chamber (103) while maintaining the conditions such as temperature and pressure in the air-tight chamber, the retort (115c) shutting off the air-tight door (115b) in an opened state from the air-tight chamber (103) when the retort is inserted into a first opening (103b) of the air-tight chamber, thus preventing condensation of the discharged gaseous material on the air-tight door.