PROBLEM TO BE SOLVED: To provide a measuring instrument of an exchange interaction force acting between a sample and a probe accurately with atomic resolving power without pull-in effects due to the proximation of the sample and the probe.
SOLUTION: For measuring an exchange interaction force acting between a sample 21 and a probe 24 installed to a vibrating cantilever 23, the sample 21 and the probe 24 are opposed to each other in proximate regions from those regions at which the wave functions of their conduction electrons start to overlap to those regions at which the wave functions of localized electrons are hardly overlapping. The cantilever 23 is provided with a piezo element 31, and control signals supplied to the piezo element 31 are generated according to the displacement of the cantilever 23. By this, the spring constant of the cantilever 23 is changed to prevent the probe 24 from being drawn to the surface of the sample 21. An exchange interaction force acting between the sample 21 and the probe 24 is measured from the control signals to the piezo element 31.