An ultrasonic flow meter comprises a flow channel (3) for a fluid to be measured to flow through, an ultrasonic transducer (5, 6) having an acoustic matching body (9c) and a piezoelectric element (9b) fixed to a metal plate (9a), an insulating damping member (11) which covers the metal plate (9a) except for the acoustic matching body (9c), a mounting portion (3b) provided in the flow channel (3), and a fixing member (13) that fixes the ultrasonic transducer (5, 6) to the mounting portion (3b), The fixing member (13) has a pressing portion (18) and an extended portion (12), and the ultrasonic transducer (5, 6) is fixed to the mounting portion (3b) by engaging a hole (16) disposed in the extended portion (12) with a hook (15) disposed on the mounting portion (3b). This structure reduces through-the-case conduction, and achieves the ultrasonic flow meter of high accuracy.