Abstract: An ultrasonic flow or current meter is disclosed in which a first ultrasonic sing-around system is connected to a pair of ultrasonic vibrators attached to a pipe through which liquid to be measured flows, a second ultrasonic sing-around system is also connected to the pair of ultrasonic vibrators, and the second ultrasonic sing-around system transmits an ultrasonic pulse in the direction opposite to that of the first ultrasonic sing-around system. In this case, the phases of the ultrasonic pulses from the first and second systems are detected, and the amount of delay of the pulse in one of the systems is controlled by the output signal to be always constant, whereby the velocity of the liquid flowing through the pipe is measured.