An ultrasonic diagnosis apparatus comprises an ultrasonic probe for scanning ultrasonic waves in a cross-sectional area of a subject, and receiving the reflected ultrasonic waves, a B-mode processor for detecting the intensity of the reflected ultrasonic waves, thereby obtaining tomographic images of the subject, an MTI processor for detecting a Doppler shift of the reflected waves, thereby obtaining blood flow data representing the velocity and direction of blood flow in the tomographic image, and a coloring processing circuit for receiving the outputs of the B-mode processor and the MTI processor and coloring the blood flow part in a monochromatic tomographic image in accordance with the velocity and direction of the blood flow. A first digital scan converter is connected between the B-mode processor and the color processing circuit and a second digital scan converter is connected between the MTI processor and the color processing circuit. The first digital scan converter changes the scan direction for of the tomographic image and produces an interpolated tomographic image. The second digital scan converter changes the scan direction of scanning blood flow data, detects aliasing of blood data, and produces an interpolated blood flow data, the interpolation being controlled in accordance with the detection of aliasing.