A manufacturing method of an absorbent article which includes a front waistline region, a back waistline region, and a crotch region positioned between the front waistline region and the back waistline region and has an elastic member (6, 6a, 6b, 6a', 6b') provided at least partially in a cross direction crossing a predetermined direction, in the front waistline region, the back waistline region, and the crotch region, the manufacturing method comprising the steps of: conveying in the predetermined direction a web (7A, 7B, 7C) in which components forming one part of the absorbent article are sequentially arranged; swinging the elastic member (6, 6a, 6b, 6a', 6b') by using a guide arm unit guiding the elastic member (6, 6a, 6b, 6a', 6b'), at a predetermined cycle in the cross direction crossing the web (7A, 7B, 7C) being conveyed in the predetermined direction; and pressing, between one pair of press rollers (130A, 130B), the web (7A, 7B, 7C) on which the elastic member (6, 6a, 6b, 6a', 6b') is arranged, wherein the guide arm unit includes a motor with a rotational shaft, the motor being a servo motor; an arm member guiding the elastic member (6, 6a, 6b, 6a', 6b') to a predetermined position on the web (7A, 7B, 7C) in the cross direction; and a speed reducer provided between the rotational shaft and a base of the arm member to make a rotational speed of the arm member slower than a rotational speed of the rotational shaft, characterised in that the speed reducer includes a sun gear positioned in a center of the speed reducer and multiple planet gears revolvable and rotatable around the sun gear, the multiple planet gears having a revolution shaft, the rotational shaft of the motor is directly connected with said sun gear, the revolution shaft of the multiple planet gears is directly connected with the base of the arm member, and the revolution shaft of the multiple planet gears and the rotational shaft of the motor are coaxially positioned. conveying in the predetermined direction a web (7A, 7B, 7C) in which components forming one part of the absorbent article are sequentially arranged; swinging the elastic member (6, 6a, 6b, 6a', 6b') by using a guide arm unit guiding the elastic member (6, 6a, 6b, 6a', 6b'), at a predetermined cycle in the cross direction crossing the web (7A, 7B, 7C) being conveyed in the predetermined direction; and pressing, between one pair of press rollers (130A, 130B), the web (7A, 7B, 7C) on which the elastic member (6, 6a, 6b, 6a', 6b') is arranged, wherein the guide arm unit includes a motor with a rotational shaft, the motor being a servo motor; an arm member guiding the elastic member (6, 6a, 6b, 6a', 6b') to a predetermined position on the web (7A, 7B, 7C) in the cross direction; and a speed reducer provided between the rotational shaft and a base of the arm member to make a rotational speed of the arm member slower than a rotational speed of the rotational shaft, a motor with a rotational shaft, the motor being a servo motor; an arm member guiding the elastic member (6, 6a, 6b, 6a', 6b') to a predetermined position on the web (7A, 7B, 7C) in the cross direction; and a speed reducer provided between the rotational shaft and a base of the arm member to make a rotational speed of the arm member slower than a rotational speed of the rotational shaft,