PROBLEM TO BE SOLVED: To evaluate a result of correlation operation based on distribution of correlation indexes.SOLUTION: An image forming part 20 forms image data of an ultrasonic wave based on collected echo data. A correlation operation part 30 calculated correlation values on respective displacements among the image data by the correlation operation among the image data based on a plurality of image data. When the correlation values on respective displacements among the image data are calculated, and the distribution of the correlation values over a plurality of the displacements is obtained, the evaluation part 40 evaluates the result of the correlation operation among the image data based on the distribution of the correlation values obtained. The evaluation part 40 extracts a plurality of extremes related to the correlation values from the distribution of the correlation values, and from the distribution of a plurality of the extremes, whether the result of the correlation operation is appropriate or not is determined.
