An ultrasound diagnostic apparatus which forms a three-dimensional bloodstream image by reference to volume data obtained from a three-dimensional space within a living organism. A modified maximum value detection method is applied along each ray. Search of a maximum value is sequentially executed from a search start point, and at a time point when a predetermined termination condition is satisfied, a maximum value which is being detected at this time point is regarded as a specific maximum value. The specific maximum value is then converted into a pixel value. The specific maximum value is a first peak and is specified even if a higher peak exists after the first peak. A three-dimensional bloodstream image is formed by a plurality of pixel values. In a portion of the three-dimensional bloodstream image in which two bloodstreams cross each other, a bloodstream located on the front side is preferentially displayed.
