PROBLEM TO BE SOLVED: To provide a production method of an underpants type absorbent article in which ultrasonic seal processing can be performed according to a layer structure on a side seal part formation planned part.SOLUTION: A production method of an underpants type absorbent article 1 comprising an absorbent body 2 and an exterior body 3, and comprising a pair of side seal parts 4, 4 on which both side parts of a ventral part A and both side parts of a back side part B are jointed, comprises a seal step for applying ultrasonic vibration to a continuum 1A of the underpants type absorbent article 1 with an ultrasonic seal device comprising an ultrasonic horn, for forming the side seal parts 4. The continuum 1A of the underpants type absorbent article comprises on a portion 40 where the side seal part is formed, plural areas 3A-3D where a number of laminated sheets or thickness is different from each other. In the seal step, plural ultrasonic horns 14A-14D are arranged corresponding to the plural areas 3A-3D in which the number of laminated sheets or thickness is different from each other, and the ultrasonic vibration is applied under a state in which positions of the ultrasonic horns 14A-14D in a direction along a thickness direction of the continuum 1A are different from each other.SELECTED DRAWING: Figure 6【課題】サイドシール部の形成予定部位の層構造に応じた超音波シール加工が可能なパンツ型吸収性物品の製造方法を提供すること。【解決手段】吸収性本体２と外装体３とを備え、腹側部Ａの両側部と背側部Ｂの両側部が接合した一対のサイドシール部４，４を有するパンツ型吸収性物品１の製造方法であり、パンツ型吸収性物品１の連続体１Ａに対して超音波ホーンを備えた超音波シール装置により超音波振動を印加してサイドシール部４を形成するシール工程を具備し、パンツ型吸収性物品の連続体１Ａは、サイドシール部を形成する部位４０に、厚み又はシートの積層枚数が異なる複数の領域３Ａ～３Ｄを有し、シール工程においては、厚み又はシートの積層枚数が異なる複数の領域３Ａ～３Ｄに対応させて複数の超音波ホーン１４Ａ～１４Ｄを配置し且つ複数の超音波ホーン１４Ａ～１４Ｄの連続体１Ａの厚み方向に沿う方向の位置を異ならせた状態下に超音波振動を印加する。【選択図】図６
