A subsurface soil purification method includes a first process of injecting a cleaning liquid, that separates a contaminant in subsurface soil from the subsurface soil and that has been warmed to a higher temperature than a groundwater temperature, into an injection well provided in the ground, and a second process of pumping up groundwater containing the cleaning liquid, in which the contaminant separated from the subsurface soil has been dissolved, from a pumping well that is provided in the ground so as to be spaced apart from the injection well.