An ultrasonic flow meter unit comprising: a measurement fluid passage through which a fluid flows; a pair of ultrasonic transducers provided on the measurement fluid passage ; a measuring circuit board including a measuring section for measuring a propagation time of an ultrasonic signal transmitted and received between the ultrasonic transducers , and a fluid flow calculating section for calculating a fluid flow based on a signal from the measuring section; a board holder for holding the measuring circuit board ; characterised in that : lead pins are connected to terminals of the ultrasonic transducers ; the pair of ultrasonic transducers are mounted to the measurement fluid passage , the board holder holding the measuring circuit board is mounted to the measurement fluid passage , and then the lead pins are connected to the measuring circuit board , one end of each of the lead pins is connected to a surface of the pair of ultrasonic transducers which is on an opposite side of a transmission/reception surface of the pair of ultrasonic transducers before the pair of ultrasonic transducers are mounted to the measurement fluid passage , and the lead pins are inserted into terminal holes of the measuring circuit board and solder-mounted thereto after the pair of ultrasonic transducers are mounted to the measurement fluid passage . a measurement fluid passage through which a fluid flows; a pair of ultrasonic transducers provided on the measurement fluid passage ; a measuring circuit board including a measuring section for measuring a propagation time of an ultrasonic signal transmitted and received between the ultrasonic transducers , and a fluid flow calculating section for calculating a fluid flow based on a signal from the measuring section; a board holder for holding the measuring circuit board ; characterised in that : lead pins are connected to terminals of the ultrasonic transducers ; the pair of ultrasonic transducers are mounted to the measurement fluid passage , the board holder holding the measuring circuit board is mounted to the measurement fluid passage , and then the lead pins are connected to the measuring circuit board , one end of each of the lead pins is connected to a surface of the pair of ultrasonic transducers which is on an opposite side of a transmission/reception surface of the pair of ultrasonic transducers before the pair of ultrasonic transducers are mounted to the measurement fluid passage , and the lead pins are inserted into terminal holes of the measuring circuit board and solder-mounted thereto after the pair of ultrasonic transducers are mounted to the measurement fluid passage . lead pins are connected to terminals of the ultrasonic transducers ; the pair of ultrasonic transducers are mounted to the measurement fluid passage , the board holder holding the measuring circuit board is mounted to the measurement fluid passage , and then the lead pins are connected to the measuring circuit board , one end of each of the lead pins is connected to a surface of the pair of ultrasonic transducers which is on an opposite side of a transmission/reception surface of the pair of ultrasonic transducers before the pair of ultrasonic transducers are mounted to the measurement fluid passage , and the lead pins are inserted into terminal holes of the measuring circuit board and solder-mounted thereto after the pair of ultrasonic transducers are mounted to the measurement fluid passage . <EOS>