Disclosed is a device for mounting an ultrasonic transducer, suitable for mounting the transducer such that it extends through a wall of a flow meter having a channel in which a fluid flows; the device includes a body in communication with an inner surface of the channel in accordance with a closed contour line that forms an interface between the inner surface of the channel and a surface of the device body, referred to as active surface, which follows the shape of the inner surface of the channel. The active surface extends continuously, and without openings, in the area delimited by the contour line. Also disclosed is a flow meter using a mounting device of this kind.