Abstract: A three-dimensional ultrasonic scanner for acquiring data concerning a three-dimensional area within a living body to be examined. In the inside of a scanner case is encased an array transducer unit. Further, at the end bottom portion of the transducer unit there is provided an array transducer composed of a plurality of transducer elements arranged in line one after another. The electronic scanning of this array transducer produces a two-dimensional scanning plane. In addition, a swinging mechanism is provided for mechanically swinging the transducer unit in a direction normal to the arrangement direction of the transducer elements. This mechanical swing movement of the transducer unit shifts the two-dimensional scanning plane to a direction normal thereto, thereby forming a three-dimensional data acquisition area within the living body. Here, a swing angle of the transducer unit is detected by an angle detector.