To carry out efficient purification treatment of a widely spread region of contaminated soil.

A purification system 1 for volatile organic compounds essentially comprises an indirect heating type rotary kiln 2 as a heating oven and an agitation aeration type drying oven 3. The drying oven 3 has a drying air flowing inlet 14, which communicates with a heating air discharging outlet 12 arranged in an outer case 5 of the kiln 2. Warm air having heated an inner case 4 is blown into an agitation space 20 of the drying oven 3 so as to cause volatile organic compounds to evaporate from low-concentration contaminated soil in the agitation space 20 through drying with the warm air and agitation, while the evaporated organic compounds can be discharged from an exhaust outlet 15 as exhaust gas.