A blood flow amount measuring apparatus includes an ultrasonic transducer for steering a region of interest of a subject to be measured with an ultrasonic beam and receiving echoes from that region. A Doppler calculation section detects a Doppler signal on a line orthogonal with the steering lines from the echo signal. The speed v of a blood flow on that line at the region of interest is calculated from the Doppler signal and thus and an amount of blood flowing through the region of interest can be evaluated from that speed and area area of the section of that blood flow.