Abstract: A cavity vibrates a sample and is combined with the sample to be equivalent to an LC circuit. An insulator electrically insulates the sample from the cavity. The insulator is placed between the sample and the cavity. A first output unit outputs, to the cavity, a first frequency signal including a frequency which causes the cavity combined with the sample to function as an equivalent circuit of an LC circuit. A second output unit outputs, to the sample and the cavity, a second frequency signal including a frequency which vibrates the sample. An amplitude detection unit detects, based on the second frequency signal, the amplitude of a reflected signal reflected from the cavity, the reflected signal being caused by the first frequency signal.