Provided are an apparatus and method for purifying contaminated soil using subcritical water. The method for purifying contaminated soil includes: (a) compressing water within a water storage tank using a high-pressure pump, and heating the water compressed by the high-pressure pump using a preheater so as to produce water in a subcritical state (i.e., subcritical water); (b) accumulating contaminated soil to be purified into a reactor; (c) enabling the subcritical water produced in step (a) to pass through the contaminated soil to be purified, which was accumulated within the reactor in step (b), at a high pressure using the high-pressure pump of step (a) to remove contaminants from the contaminated soil to be purified; (d) cooling high-temperature processing water containing the contaminants of step (C) using a heat exchanger; and (e) separating the contaminants from the processing water which contains the contaminants and which is cooled by the heat exchanger in step (d) by means of specific gravity using a separator.