To precisely discriminate respective strata (clay, silt, sand, gravel and others) of a ground uninvestigated point.

A factor ai to respective explanation variables is formed, by performing a multiple regression analysis for a plurality of equations, by forming the plurality of equations on the same stratum, by imparting the same objective variable N to the same stratum, with an engineering characteristic Xi of the ground as the explanation variable. An engineering characteristic ^Xi of the ground of a desired depth part of an uninvestigated point, is estimated from an engineering characteristic of the ground of an investigated point. The factor ai to the respective explanation variables is applied to the estimated engineering characteristic ^Xi of the ground. What is the stratum of the depth part, is discriminated by whether or not the generated objective variable is near to the objective variable N imparted to which stratum.