A flow rate measurement method, characterized in that: the method comprises (a) repeating, a predetermined number of times, a step of transmitting an ultrasonic wave into a fluid pulsatingly flowing through a flow passage, receiving the ultrasonic wave, and recording an ultrasonic wave transmission and receipt-indicative signal indicative of the transmission and receipt of the ultrasonic wave; and a step of recording a timing signal (2*) indicative of a timing at which the transmission and receipt of the ultrasonic wave have been performed, or (b) repeating, a predetermined number of times, a step of transmitting a timing signal (2*) at a predetermined timing; and a step of, in response to the transmitted timing signal (2*), transmitting an ultrasonic wave into a fluid pulsatingly flowing through a flow passage, receiving the ultrasonic wave, and recording an ultrasonic wave transmission and receipt-indicative signal indicative of the transmission and receipt of the ultrasonic wave, whereafter the method further comprises: based on at least part of the recorded ultrasonic wave transmission and receipt-indicative signals, determining flow rates corresponding to the at least part of the ultrasonic wave transmission and receipt-indicative signal; based on at least part of the timing signals (2*), signals, determining ultrasonic wave transmission and receipt timings (3*) corresponding to the at least part of the timing signals (2*); and based on the determined respective flow rates and the determined respective transmission and receipt timings (3*), determining a time-dependent fluctuation in the flow rate of the fluid by associating the respective flow rates with their respective transmission and receipt timings (3*). the method comprises (a) repeating, a predetermined number of times, a step of transmitting an ultrasonic wave into a fluid pulsatingly flowing through a flow passage, receiving the ultrasonic wave, and recording an ultrasonic wave transmission and receipt-indicative signal indicative of the transmission and receipt of the ultrasonic wave; and a step of recording a timing signal (2*) indicative of a timing at which the transmission and receipt of the ultrasonic wave have been performed, or (b) repeating, a predetermined number of times, a step of transmitting a timing signal (2*) at a predetermined timing; and a step of, in response to the transmitted timing signal (2*), transmitting an ultrasonic wave into a fluid pulsatingly flowing through a flow passage, receiving the ultrasonic wave, and recording an ultrasonic wave transmission and receipt-indicative signal indicative of the transmission and receipt of the ultrasonic wave, (a) repeating, a predetermined number of times, a step of transmitting an ultrasonic wave into a fluid pulsatingly flowing through a flow passage, receiving the ultrasonic wave, and recording an ultrasonic wave transmission and receipt-indicative signal indicative of the transmission and receipt of the ultrasonic wave; and a step of recording a timing signal (2*) indicative of a timing at which the transmission and receipt of the ultrasonic wave have been performed, or (b) repeating, a predetermined number of times, a step of transmitting a timing signal (2*) at a predetermined timing; and a step of, in response to the transmitted timing signal (2*), transmitting an ultrasonic wave into a fluid pulsatingly flowing through a flow passage, receiving the ultrasonic wave, and recording an ultrasonic wave transmission and receipt-indicative signal indicative of the transmission and receipt of the ultrasonic wave, whereafter the method further comprises: based on at least part of the recorded ultrasonic wave transmission and receipt-indicative signals, determining flow rates corresponding to the at least part of the ultrasonic wave transmission and receipt-indicative signal; based on at least part of the timing signals (2*), signals, determining ultrasonic wave transmission and receipt timings (3*) corresponding to the at least part of the timing signals (2*); and based on the determined respective flow rates and the determined respective transmission and receipt timings (3*), determining a time-dependent fluctuation in the flow rate of the fluid by associating the respective flow rates with their respective transmission and receipt timings (3*). based on at least part of the recorded ultrasonic wave transmission and receipt-indicative signals, determining flow rates corresponding to the at least part of the ultrasonic wave transmission and receipt-indicative signal; based on at least part of the timing signals (2*), signals, determining ultrasonic wave transmission and receipt timings (3*) corresponding to the at least part of the timing signals (2*); and based on the determined respective flow rates and the determined respective transmission and receipt timings (3*), determining a time-dependent fluctuation in the flow rate of the fluid by associating the respective flow rates with their respective transmission and receipt timings (3*).