band pass filter 80 b becomes a signal moderately varying at the edge portion on the sample surface as shown in fig1 b this band pass signal sm is converted into a digital signal by an a d converter 82 b and memorized in an image memory 83 b a band pass signal sl passed through the band pass filter 80 c becomes a signal corresponding to a surface geometry of the sample as shown in fig1 c of the same figure this band pass signal sl is converted into a digital signal by an a d converter 83 c and memorized in an image memory 83 c according to the present embodiment the surface geometry of a sample can be displayed in hue different depending on its space frequency for example the edge portion forming abruptly roughness or the like is displayed in white by superposing all the color image data band pass signals thereby enabling contour emphasis further the concave portion and the convex portion are different in intensity of the band pass signal sl and hence in color concentration as shown in fig1 c so that both are easily to distinguished furthermore a portion adjacent the edge gradually varies in display color from white to green and to red since this functions as a shadow a three dimensional display becomes possible fig9 is a block diagram of a signal processing system of a scanning probe microscope according to a third embodiment of the present invention wherein the same reference numerals as those stated before denote the same or equivalent parts in the present embodiment a strain signal s 1 output by a differential amplifier 74 is directly input to a band pass filter 80 d while an observed image signal s 3 output by a.