Abstract: An ultrasonic flow or current meter having at least one pair of transducers, a transceiver which applies a pulse signal to one of the transducers to produce an ultrasonic pulse wave, the other transducer receiving the ultrasonic pulse wave and producing the corresponding electrical signal, a reference pulse signal generator, a counter for counting the pulse signals from the reference signal generator in relation to the corresponding electrical signal, and a logical operational circuit. The logical operational circuit is supplied with the output signal from the counter and calculates a difference between a first reciprocal of a time required for the ultrasonic pulse wave to propagate from one of the pair of transducers to the other transducer and a second reciprocal of a time required for the ultrasonic pulse wave to propagate in the reverse direction between the pair of transducers, with the difference between the first and second reciprocals being multiplied by a constant.