A fixing member is fixed to a beverage pack in a state in which a through-hole and an opening are aligned. Next, the pointed end of an adapter body is inserted into the opening through the through-hole. This causes the pointed end to puncture a film and pass through the opening, but a flange serves as a stopper so that just the pointed end is inserted into the beverage pack. At this point the surrounding area is kept liquid-tight by a seal, and the adapter body is prevented from falling out by ridges provided to this. One end of a tube is connected to a joint of the adapter body. A catheter is connected to the other end of this tube, allowing a nutritional beverage contained in the beverage pack to be discharged directly from the catheter.