PURPOSE: To obtain composite vibration wherein longitudinal and lateral componets are synthesized on a radiation surface when longitudinal vibration is applied to an input surface by providing an opening and/or a notch inclined with respect to a longitudinal vibration direction to a horn main body wherein the longitudinal dimension between the input surface and the radiation surface opposed thereto is set to a specified dimension.

CONSTITUTION: A horn main body 2 has a plate shape and the longitudinal dimension L thereof between an input surface 3 receiving ultrasonic longitudinal vibration by the male screw part 3a provided to the central part thereof and a radiation surface 4 from which composite vibration is taken out is set to 1/4-1/2 the frequency λ of longitudinal vibration F. A slit 5 inclined at an angle θ with respect to the direction of longitudinal vibration F in a lateral direction is provided to the central part of the surface of the horn main body 2. By this constitution, composite vibration wherein longitudinal and lateral components are synthesized can be obtained on the radiation surface 4. Further, notches are provided to both end parts of the horn main body 2 in the lateral direction thereof at the angle θ and, when the horn main body 2 is formed into a parallelogram as a whole, displacement can be made almost uniform over the whole of the radiation surface 4 even when the dimension in the lateral direction is λ/4 or more.