The present invention obtains certainty of the blood-flow velocity information that is estimated in the blood-flow mapping display. The signal processor in the ultrasound imager is provided with a Doppler velocity operation part configured to calculate a Doppler velocity from echo signals by using the Doppler effect, and a first blood-flow velocity operation part configured to generate a tissue tomographic image from the echo signals and calculate a blood-flow velocity of a predetermined portion from a motion of the tissue, on the basis of the tissue tomographic image. It is further provided with a second blood-flow velocity operation part configured to calculate the blood-flow velocity of the predetermined portion by using the Doppler velocity calculated by the Doppler velocity operation part. Then, a coincidence degree is calculated between the blood-flow velocity calculated by the first velocity operation part and the blood-flow velocity calculated by the second velocity operation part, as to the predetermined portion, and according to the coincidence degree, certainty/reliability of the blood-flow velocity information is obtained and displayed.
