Abstract: A phase difference comparison type of ultrasonic velocity meter repeatingly transmitting acoustic waves in the form of pulses at alternate time intervals: T-T.sub.S and T+T.sub.S, receiving reflected waves generated by the transmission of these waves and reflected on an object, forming first and second mixed waves by mixing the reception signal obtained from the reflected waves with two reference waves having phases shifted 90 degrees from each other, detecting the phase difference between the present vectors representing the first and second mixed waves and similar vectors which have been obtained with respect to the preceding pulse transmission, detecting the phase difference Q between the phase difference caused in relation to the time interval T-T.sub.S and the phase difference caused in relation to the time interval T+T.sub.S with respect to a phase difference obtained each time a pulse is transmitted, and calculating the Droppler shift angle frequency .omega.d from .omega.d=Q/2T.sub.S.