An ultrasonic horn includes: a vertical vibration generating portion in which a first ultrasonic vibrator is mounted inside; a horn portion extending forward from the vertical vibration generating portion, amplifying an ultrasonic vibration generated by the vertical vibration generating portion, and to which a capillary is mounted at a front end portion; and a torsional vibration generating portion extending rearward from the vertical vibration generating portion. The torsional vibration generating portion includes: a rod-shaped body; vibration members arranged axisymmetrically around a central axis; second ultrasonic vibrators sandwiched between the rod-shaped body and the vibration members such that a vibration direction is a circumferential direction; and bolts pressurizing the second ultrasonic vibrators.

A horn has knurl-shaped protrusions and recesses that are formed of a plurality of protrusions, and are formed on a first end surface. Among the plurality of protrusions, at least a pair of protrusions arranged symmetrically at both outermost ends in a direction along a vibration direction are asymmetrical surface protrusions. In each of the asymmetrical surface protrusions, an angle value of an outer inclination angle is smaller than an angle value of an inner inclination angle.