Provided is an ultrasonic welding apparatus that performs an ultrasonic welding process to a sheet-like member associated with an absorbent article, the sheet-like member being transported while being wound onto an outer circumferential face of a rotating member that rotates about its central axis. The ultrasonic welding apparatus includes an ultrasonic processing unit that rotates about the central axis together with the rotating member. The ultrasonic processing unit includes a horn that vibrates ultrasonically and an anvil between which and the horn the sheet-like member is sandwiched. At least either one ultrasonic processing member of the horn and the anvil is guided so as to reciprocate in a CD direction intersecting a transport direction of the sheet-like member, and the one ultrasonic processing member reciprocates in the CD direction with respect to a part wound around the rotating member in the sheet-like member. The outer circumferential face of the rotating member includes a first section and a second section at positions different from each other in the CD direction. The ultrasonic welding apparatus further comprises an ultrasonic-energy regulating unit making an amount (J/m) of ultrasonic energy applied per unit length in the CD direction when the ultrasonic processing member passes through the first section on either one of a forward path and a return path of the reciprocation different from an amount (J/m) of ultrasonic energy applied per unit length in the CD direction when the ultrasonic processing member passes through the second section on either one of the forward path and the return path.
