PURPOSE: To form a convergence point with less phase dislocation by receiving a pair of signals, i.e., a signal from a constant vibrator and a signal from a vibrator selected from the position near it toward the position remote therefrom, and correcting the specific delay time on the basis of the correlation function information calculated by a correlation calculating means using that pair of received signals.

CONSTITUTION: When photographing is started with a probe 2, a CPU 35 executes photographing, for ex., a B-mode image, and a delay control part 13 makes delay control of an excite signal generating part 11 and a signal receipt delay circuit 15 on the basis of specific delay time information stored in the delay control part. A B-mode image is displayed in a display part 14 when the probe 2 makes the first run of OF B-mode scan. A correcting system 20 calculates the correction delay time on the basis of signal from No.1 multiplexer 3, and the specified delay time information is corrected to a delay time in accordance with a vital body transfer medium. On the basis thereof, the delay control part 13 makes delay control, and the probe 2 makes the second run and thereafter of OF B-mode image scanning. Thereby a convergence point with less phase dislocation is formed, and a B-mode image with resolution not sunk is displayed on the display 14.