The present invention provides a fast-operating and stable scanning probe microscope configured to detect the interaction between a probe and a sample to avoid generation of a harmonic component. An oscillation circuit (31) generates an excitation phase signal indicative of the phase of an excitation signal. An excitation signal generation circuit (33) generates an excitation signal from the excitation phase signal. A complex signal generation circuit (35) generates a complex signal from a displacement signal. A vector calculation circuit (37) calculates the argument of the complex signal. A subtracting phase comparator (39) compares the argument with the phase of the excitation phase signal by subtraction. The amount of the interaction between a probe device and a sample is obtained using the subtracting phase comparator (39). The result of the comparison carried out by the subtracting phase comparator (39) may be output as a difference in phase between the displacement signal and the excitation signal. Moreover, a loop filter may be provided to form a phase locked loop, and a frequency signal may be provided which is indicative of a variation in the resonant frequency of the probe device.