A barrel support device supports a barrel rotationally about an axis of the barrel with the axis being arranged vertically and an opening of the barrel through which a plunger rod is inserted being directed upward. A chuck of a plunger rod support device holds the plunger rod in a first holding state in which the plunger rod is prevented from rotating about and sliding along its axis and inserts it into the barrel. Then, the chuck enters a second holding state in which the plunger rod is prevented from rotating about its axis but is not prevented from sliding along its axis. A load application device places a load acting downward on the plunger rod, and a rotation application device rotates the barrel in a direction in which the plunger rod is screwed into a gasket in the barrel.
