In order to be able to couple as great a fraction as possible of ultrasonic measuring signals into a medium to be measured, an ultrasonic sensor is provided with a cup-shape and includes a housing and an oscillatable unit for producing the ultrasonic signals. The oscillatable unit is composed of a plurality of components and is so embodied that it has a node plane, which is oriented essentially perpendicularly to the radiating or receiving direction of the ultrasonic measuring signals. At least a portion of the outer surface of the oscillatable unit is connected with the housing in the region of the node plane of the oscillatable unit.