PURPOSE: To realize an ultrasonic diagnostic apparatus which measures an ultrasonic propagation speed of a tissue in a noninvasive manner from outside.

CONSTITUTION: A transmitting vibrator 1 transmits an ultrasonic wave varying an angle θi of emission at an angle adjustor 13 and a receiving vibrator 2 receives the ultrasonic wave with an angle θj being varied by an angle adjustor 14. Time tij elapsed during the period is measured with a time measuring circuit 17 to be stored into a tij memory 18. An assumed sound speed distribution chart is stored into the sound speed memory 19 and a sound line tracking computation circuit 20 sets a sound line path varying an angle of wave reception of the transmitting/receiving vibrators on the sound speed memory 19 based on the sound speed distribution chart while a required time tij of the operation is stored into a tij' memory 21. A comparator 22 inputs an error data by comparison between the tij and tij' into a controller 23, with which an assumed sound speed distribution stored in the sound speed memory 19 is corrected to minimize the error data inputted thereby determining a sound speed from a sound speed distribution obtained finally.