A system for measuring a peak frequency of a signal applies a Maximum Entropy Method (MEM) to the signal obtained through transmission and reception of an electromagnetic wave to a subject to obtain a frequency of a peak component to be measured, thus permitting to make an appropriate assessment on a state of the subject. A signal analysis unit performs a spectrum estimation utilizing the MEM applied to a signal part of the phase difference signal with a predetermined short analysis duration, from a phase difference signal obtained by an electromagnetic wave transmitting and receiving unit, to obtain a frequency indicative of occurrence frequency of the peak component, and conducts repeatedly the same process, while shifting a position to be analyzed, corresponding to the analysis duration, thus introducing continuously the frequency. It is therefore possible to know a transition with time of the frequency of the peak component.
