To solve the problem that a method to obtain three-dimensional (3-D) images by ultrasound is not appropriate for watching relatively fast movements made by the heart, or the like, caused by the method which requires much time for ultrasound beam scanning and causes difficulty in obtaining dynamic images.

Drive circuits 2 are respectively connected to a plurality of elements 1a, 1b and 1c of an ultrasonic two-dimensional (2-D) array transducer 1, and modulation circuits 3 for inputting different modulating signals are connected to the drive circuits 2, respectively. A receiving amplifier 4 is connected to a receiving element 1A which is an element of the ultrasonic 2-D array transducer 1. An A/D converter 5 for converting received analog signals into digital signals is connected to the receiving amplifier 4, and the digital signals converted by the A/D converter 5 are stored in a memory 6 sequentially. The digital signals stored in the memory 6 are read out sequentially, and are demodulated by a demodulation circuit 8 and displayed on a display device 9 of a personal computer 7.