PROBLEM TO BE SOLVED: To perform a high speed approach when the distance between a probe and a sample is large and a low speed approach when the probe comes closer to the sample by finding the distance between the probe of a cantilever and the sample utilizing changing characteristic of reflected light on a photodetector from others than the rear of a cantilever to protect the probe of the cantilever and the sample while shortening the approaching time. SOLUTION: A signal Sz from a probe displacement signal detecting section 46 is differentiated by a differential computation section 57 within a probe displacement signal change detection mechanism 48 and the results are outputted to a threshold judging section 58. When an output signal d(Sz)/dt of the differential computation section 57 is judged to exceed a specified threshold ref1 at the threshold judging section 58, a stop command is sent to a motor 34 through a motor driver 50 from an approach stopping section 59 and approaching by a coarse action mechanism 33 is stopped. At the same time, a specified voltage is applied from the approaching section 59 and a piezo-electric body 31 shrinker in the direction Z so that a probe 41 of a cantilever 42 separates from the surface of a sample 36.
