Abstract: An outlet stopper includes a cap part made of a resin and having a cylinder which has a screw thread on a side face thereof, and an outlet part made of a resin and having a disk flange which has a bottom face thereof coated with an adhesive. The disk flange has a hole at a center portion thereof. The outlet part has another cylinder which is placed on top of the disk flange and has a screw thread on a side face thereof which fits the screw thread on the cylinder in the cap part. An opening blade is fixed to the inside of the cap part, and a stopping ring which has a protrusion projected outward therefrom has a break therein for opening the ring and for stopping the insertion of the cap part and the outlet part into each other before reaching a fully screwed-in position. The outlet stopper can be easily attached with the adhesive to a package commercially available in a pouch form.