PURPOSE: To obtain an image having high resolving power and a good S/N ratio over a wide range in a distance direction, by converging one of receiving sensitivity distributions of transmission ultrasonic beam and a reflected wave.

CONSTITUTION: A probe 1 is inergized by a pulser 2 and performs transmission so that the position of ultrasonic beam in a living body being a region to be imaged successively moves. The energization of the probe 1 is performed by converging ultrasonic beam by controlling the driving timing of each vibrator and the transmission of an ultrasonic wave is performed by repeating (2N+1) times at a certain position while the repetition of a reflected wave is performed (2N+ 1) times while a receiving position is changed within the range of N-numbers of vibrators corresponding to transmission. In this case, the values of N are determined by the expanse of the receiving sensitivity of each vibrator. Hologram data crossing at right angles subjected to phase detection by a phase detector 5 are converted by A/D converters 6, 7 and stored in an image memory 11 through a computer CPU 10 and, thereafter, the imaging information of a living body calculated by aperture synthesizing processing in CPU 10 is stored in buffer 12 and displayed on monitor 14.