The method 100 includes an ultrasonic vibrating device 110 configured to applyultrasonic vibration to the predeterminedregion 50A, an anvil roller 120 facing the ultrasonic vibrating device 110with the superimposed continua of the frontwaistline portions and the back waistline portions interposed therebetween,and including a protrusion 122 configured to press thecontinua in the predetermined region 50A between the anvil roller 120 and theultrasonic vibrating device 110, a motor 130 configuredto rotate the anvil roller 120, a belt 140 configured to connect the anvilroller 120 and the motor 130 and to be driven bythe motor 130, and a pressing mechanism 150 configured to press the belt 140in a cross direction perpendicular to a drivingdirection of the belt 140.
