An ultrasonic diagnostic apparatus according to the present invention includes: a transmitting section that generates a drive signal to drive a probe in order to transmit an ultrasonic wave toward a subject to be deformed periodically under stress; a receiving section for receiving an echo, produced when the ultrasonic wave is reflected from the subject, at the probe to generate a received echo signal; a computing section for figuring out a thickness change waveform, representing a variation in distance between two arbitrary measuring points on the subject, based on the received echo signal; and a reference waveform generating section for outputting a reference waveform. The apparatus obtains subject's internal information by comparing the thickness change waveform and the reference waveform to each other.