A nutrient solution is reduced with a reducing agent, and introduced into a
contaminated object. Alternatively, groundwater reduced with a reducing
agent is introduced into the contaminated object. Groundwater is contacted
with the reducing agent while being circulated between an aquifer and a
housing. A nutrient source for heterotrophic anaerobic microorganism may
also be introduced into the contaminated object. The contaminated object
contaminated with halogenated organic compounds can be purified
efficiently and easily.