PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter that is able to accurately measure a propagation time even if distortion occurs in a reception waveform due to influence from vibration noise or the like.SOLUTION: In a flow rate measurement device, variation arithmetic means 16 obtains a difference between a measured time value in a previous unit measuring step and a measured time value in a present unit measuring step obtained by timer means 10. If the difference value is equal to a cycle of a reception signal amplified by amplification means 6, erroneous measurement determination means 17 determines the present measured time value is erroneous, selection means 12 selects only effective values from output of the timer means 10, and propagation time arithmetic means 13 obtains a propagation time using the selected data.
