When a liquid surface is detected based on a detection signal from a photodetector during the approaching operation, a photodetector movement processor moves the photodetector to a position where reflected light from a cantilever is incident with the cantilever being in liquid. When the reflected light from the cantilever is incident on the photodetector during the approaching operation continued after the movement of the photodetector by the photodetector movement processor, an optical axis adjustment processor adjusts an optical axis of the reflected light incident on the photodetector. When a surface of a solid sample is detected based on a detection signal from the photodetector during the approaching operation continued after the adjustment of the optical axis by the optical axis adjustment processor, an approaching processor stops the approaching operation.