[Object]To provide a method and an apparatus capable of measuring a pulsatingly fluctuating flow rate under a general condition, without needing electrical conductivity for a fluid, and without allowing a phase lag corresponding to a calculation time or attenuation or a phase lag resulting from a relation between pressure difference and flow rate to occur.[Means to Accomplish the Object]Ultrasonic waves are repeatedly transmitted with respect to a pulsatingly fluctuating fluid, while the ultrasonic wave being received, and a signal indicative of the transmission and receipt, and a signal indicative of a timing of the transmission and receipt are recorded. Alternatively, the ultrasonic wave is transmitted and received based on a preliminarily set timing signal, and the signal indicative of the transmission and receipt is recorded. These signals are used to determine flow rates and transmission and receipt timings to plot a pulsating fluctuation. In the case of performing transmission and receipt of the ultrasonic wave based on the preliminarily set timing signal, it is preferable to phase-synchronize the timing signal with a pulsation reference signal.