A frequency shift Δf obtained by an FM-AFM can be expressed by a simple linear coupling of a ΔfLR derived from a long-range interaction force and a ΔfSR derived from a short-range interaction force. Given this factor, a Δf curve on an atomic defect and a Δf curve on a target atom on the sample surface are each measured for only a relatively short range scale (S1 and S2), and a difference Δf curve of those two curves is obtained (S3). Since the difference Δf curve is derived only from a short-range interaction force, a known conversion operation is applied to this curve obtain an F curve which illustrates the relationship between the force and the distance Z, and then the short-range interaction force on the target atom is obtained from the F curve (S4). Since the range scale in measuring the Δf curve can be narrowed, the measurement time can be shortened, and since the conversion from the Δf curve into F curve is required only once, the computational time can also be shortened. Consequently, in obtaining the short-range interaction force which acts between the atom on the sample surface and the probe, the time required for the Δf curve's measurement and the computational time are shortened, which leads to accuracy improvement and throughput enhancement.