A device for manufacturing a disposable wearing article in which by supplying at least a single continuous web as a member of a continuously manufactured disposable wearing article in a machine direction, and by supplying a continuous elastic member while swinging the elastic member in a crossing direction along a widthwise direction of the web that is the direction crossing the machine direction, the elastic member is mounted in an extended state on the web, the device comprising: a pair of press rolls, having a rotation spindle extending in the crossing direction, configured to press the elastic member and the web while rotating along the machine direction; and a guide arm unit configured to supply the elastic member from the front of the pair of press rolls in the machine direction between the pair of press rolls while swinging the elastic member in the crossing direction, wherein the guide arm unit comprises: a motor, having a motor turning spindle, configured to enable reversal of a turning direction of the motor turning spindle; and an arm member in which a through hole from which the elastic member is inserted is formed, and the arm member is swung, in the crossing direction, around an arm turning spindle turned by the motor, characterized in that in a viewpoint from above a straight line that passes through the center of a widthwise direction of a lower end of the through hole and is parallel to the arm turning spindle, the center of the widthwise direction of the lower end of the through hole is positioned on one side with a reference of a nip line (Ln) showing a position where a peripheral surface of one press roll configuring the pair of press rolls is closest to the peripheral surface of the other press roll, at both a central position where the arm member does not swing and at a swinging end where the arm member swings the most, and the position of the through hole at the swinging end is closer to the nip line (Ln) than the position of the through hole at the central position. a pair of press rolls, having a rotation spindle extending in the crossing direction, configured to press the elastic member and the web while rotating along the machine direction; and a guide arm unit configured to supply the elastic member from the front of the pair of press rolls in the machine direction between the pair of press rolls while swinging the elastic member in the crossing direction, wherein the guide arm unit comprises: a motor, having a motor turning spindle, configured to enable reversal of a turning direction of the motor turning spindle; and an arm member in which a through hole from which the elastic member is inserted is formed, and the arm member is swung, in the crossing direction, around an arm turning spindle turned by the motor, characterized in that in a viewpoint from above a straight line that passes through the center of a widthwise direction of a lower end of the through hole and is parallel to the arm turning spindle, the center of the widthwise direction of the lower end of the through hole is positioned on one side with a reference of a nip line (Ln) showing a position where a peripheral surface of one press roll configuring the pair of press rolls is closest to the peripheral surface of the other press roll, at both a central position where the arm member does not swing and at a swinging end where the arm member swings the most, and the position of the through hole at the swinging end is closer to the nip line (Ln) than the position of the through hole at the central position. a motor, having a motor turning spindle, configured to enable reversal of a turning direction of the motor turning spindle; and an arm member in which a through hole from which the elastic member is inserted is formed, and the arm member is swung, in the crossing direction, around an arm turning spindle turned by the motor, characterized in that