Based on the characteristic of the Wide-beam ultrasonic flowmeter, automatic gain control amplifier and the tracking band-pass filter are devised.

Upon reception of a burst detection start trigger signal, a gain control signal is output to an automatic gain control amplifier (201) so as to perform amplification with a maximum value.

Wideband amplifier, realized by the technology of automatic gain control (AGC), is used widely in radar system and other correlative electronic fields.