PURPOSE: To enhance fine adjustment detecting sensitivity of a scanning type probe microscope and to accurately measure finely adjusting coordinates by calculating a moving displacement of a flexible system from a detection signal from a single photoreceiving surface of a photoreceiver or detection signal of multisegment photoreceiving surfaces.

CONSTITUTION: A laser light emitted from a focused beam light source 11 is reflected on an outer spherical mirror, and received by a quarter or split-half photoreceiving surface type photoreceiver 12. Photoelectric conversion outputs of the split photoreceiving regions are input to a signal differential amplifier 14 to detect axial output differences,ΔEx-ΔEz. These differences are all input to a calculator 18 to be calculated. A controller 16 calculates a deflection of a laser light spot of the surface of the photoreceiver 12 from the difference of the calculator 18, and obtains a displacement of a piezoelectric element l from the deflections of the respective axial directions. This relation is previously measured, its formula is obtained by the controller 16, and finely adjusting coordinates at the time of operating an external force of arbitrary magnitude can be accurately calculated from measured values of the ΔEx-ΔEz.