To construct a system for improving soil environment in a simple structure and compact facility.

A soil cleaning method comprises the steps of: supplying a pressurized air from a blower 10 by an air injection pipe 11 from an aquifer 3 to a soil layer 2; making the pressurized air act on an oil reservoir 4 reserved above the aquifer 3; turning the oil in the oil reservoir 4 into a volatile or misty state by a decomposition action of microorganisms; volatilizing oil content reserved in the soil layer 2 as well to be taken in a gas flow-in part 21 in a cleaning unit 20 in a concentrated manner; adsorbing the oil content in a treatment part 22 located above the gas flow-in part 21 to be cleaned; and releasing the detoxified air to the atmosphere.