A method for measuring a mechanical property of a subject includes using an ultrasonic transducer to apply ultrasonic vibration pulses to a vibration origin in the subject in an on-off time sequence in order to impart a harmonic motion at a prescribed frequency to the subject, and when the vibration pulses are off, using the same transducer to apply ultrasonic detection pulses to a motion detection point and to receive echo signals therefrom in order to sense the harmonic motion on the subject at the motion detection point. From the harmonic signal information, a harmonic signal is detected and a characteristic such as amplitude or phase of the detected harmonic signal is measured. The mechanical property is calculated using the measured characteristic using for example a wave speed dispersion method.