Provided are a surface state measuring device which can measure an alternating force of an arbitrary frequency and which is excellent in spatial resolution, and a surface state measuring method using the device. This surface state measuring device measures the surface state of a sample by detecting the modulation of the oscillation of a probe arranged above the sample. The measuring device comprises: a cantilever having a probe near a free end; an excitation mechanism for exciting the cantilever; a scanning mechanism for making the probe scan the sample by moving the probe and the sample relative to each other; and alternating force generator for generating an alternating force of an arbitrary frequency in a space; and a modulation measuring mechanism for measuring the degree of frequency modulation or amplitude modulation of the oscillations of the probe, which are generated by the alternating force.