An ultrasonic horn is provided with: a vibration generating unit configured to generate longitudinal vibration having a frequency in the ultrasonic band on the basis of a signal having a frequency in the ultrasonic band input from an oscillator; a vibration amplifying unit configured to amplify the vibration generating unit while transmitting the longitudinal vibration from the vibration generating unit; and a longitudinal-torsional vibration conversion slit unit having slits formed in a groove-like shape on the surfaces of the vibration amplifying unit and configured to convert the longitudinal vibration into torsional vibration. The vibration amplifying unit has a polygonal shape in a plane view, and has a plurality of surfaces provided with slits along with a surface not provided with slits.