PURPOSE: An ultrasonic flowmeter is provided to reduce an affection due to a phase difference by using a pair of ultrasonic oscillators. CONSTITUTION: The ultrasonic flowmeter comprises a pair of ultrasonic oscillators (10, 11); a unit (12) for measuring the time period for which ultrasonic waves propagate between the paired ultrasonic oscillators (10, 11); and a unit (13) for computing the rate of a fluid flowing through a flow rate measuring section (7) on the basis of the output of the measuring unit. The flow rate measuring section (7) and the pair of ultrasonic oscillators (10, 11) are so constructed as to reduce the influences of waves reflected by the wall of the flow rate measuring unit on the measurements.
