An ultrasonic continuous wave blood flowmeter using Doppler effect analysis includes a filter having a cut-off frequency determined in part by a manually selected zero shift value. A tranducing device, in the flowmeter includes a transmission element and a reception element, the transmission element transducing an electric transmission signal into an ultrasonic signal to irradiate a living body and the reception element transducing a reflected ultrasonic signal into an electric reception signal. A detecting circuit is operatively connected to the transducing device for orthogonally detecting the electric reception signal and outputting a Doppler detection signal. A filter circuit is operatively connected to the detecting circuit for cutting high frequency components of the Doppler detection signal based on the cut-off frequency and outputting an analog signal. A converting circuit is operatively connected to the filter circuit for converting the analog signal of the filter circuit to a digital signal based on a Doppler sampling frequency having a continuous wave. A transforming circuit is operatively connected to the converting circuit for analyzing the digital signal and obtaining a Doppler frequency spectrum based on a Fourier transform method. A control circuit is operatively connected to the filter circuit for controlling the cut-off frequency based on the Doppler sampling frequency and the zero shift value.
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