In the present invention, a distance spectrum computation unit removes the direct current component from the intensity distribution of the frequency of the combined wave detected by a standing wave detection unit and subjects the intensity distribution to a Fourier transform to obtain a distance spectrum. A differential detection unit subtracts a base period distance spectrum from the aforementioned distance spectrum to calculate the difference between the distance spectra, and this differential distance spectrum is obtained over time. A detection unit detects the state just before freezing by means of the decrease of the proportion of the water content in a food material serving as the measurement target, on the basis that the peak intensity of the differential distance spectrum changes on the basis of a change in the permittivity of the measurement target. When the state just before freezing is detected by the detection unit, a control unit controls the state of the food material to maintain a non-frozen state. As a result, it is possible to measure changes over time to the water content, and the like, of the measurement target, thus enabling, for example, maintenance of food freshness, discovery of abnormal sites in the human body, and detection of the activity status of a plant and the sweating state of a person.Dans la présente invention, une unité de calcul de spectre de distance supprime la composante de courant continu de la distribution dintensité de la fréquence de londe combinée détectée par une unité de détection donde stationnaire et soumet la distribution dintensité à une transformée de Fourier pour obtenir un spectre de distance. Une unité de détection différentielle soustrait un spectre de distance de période de base au spectre de distance mentionné ci-dessus pour calculer la différence entre les spectres de distance, et ce spectre de distance différentiel est obtenu au cours du temps. Une unité de détection détecte létat juste avant la congélation a
