The object of the present invention is to realize a low-invasive underground exploration apparatus, system, and method which are capable of specifying the kind, three-dimensional position, and amount of a substance present in the ground. The underground exploration apparatus, system, and method includes: measuring, at multiple points, a high frequency voltage that appears upon conduction of high frequency current through the ground to obtain measurement results at two or more frequency levels; employing an ground model using the finite element method, the boundary element method, an impedance network, or the like to estimate a substance in the ground by changing unknown quantities of the ground model such as local dielectric constant and electric conductivity so as to make an error between the actual measured value and the calculated value smaller; and displaying input information of the ground model and results of the estimation processing two-dimensionally or three-dimensionally.