A probe needle is successively moved to a plurality of measurement points set in a measurement region on a sample so as to measure a z-displacement amount. An excitation control unit feedback-controls a piezoelectric element so that a vibration amplitude of a cantilever is constant in accordance with the detection output by a displacement detection unit. Moreover, a vertical displacement control unit feedback-controls a vertical position scan unit so as to obtain a constant distance between the probe needle and the sample according to a frequency shift by a frequency detection unit. When changes of outputs of two feedback loops at a certain measurement point are both within a predetermined range, a main control unit issues an instruction to a horizontal position control unit to rapidly move to the next measurement point. As a result, it is possible to adaptively decide such a measurement time that both of the two feedback controls at respective measurement points are established. This eliminates an unnecessary measurement time, which in turn reduces the time required for creating one convex/concave image as compared to the conventional technique and improves the throughput.