To provide an ultrasonic imaging device equipped with a constitutionally simple beam former for transmitting/receiving ultrasonic waves for three- dimensional imaging.

An ultrasonic transducer array has a single transmitting aperture 402, which is composed of ultrasonic vibrator arrays on longitudinal and horizontal centerlines of a central square area, and a plurality of receiving apertures 502-508, which are composed of the ultrasonic vibrator arrays on a pair of diagonal lines in each of the plurality of square areas. By means of the ultrasonic transducer array, the ultrasonic waves are transmitted repeatedly in one direction from the transmitting aperture 402 times of the same number as that of the receiving apertures 502-508, and echoes are received repeatedly in one direction while making the receiving apertures 502-508 changed each time the ultrasonic waves are transmitted, for the purpose of merging receiving signals by the addition of received echo signals. These are performed sequentially with a change in direction so as to scan an imaging range three-dimensionally.