Spout stopper and packaging container

A spout stopper comprising:

• a stopper body including a cylindrical side wall having an external screw formed on an outer circumferential surface thereof;
• and
• a cap to be mounted from an upper end side that is one end of the side wall of the stopper body, the cap including a top surface and a side wall having an internal screw formed on an inner circumferential surface thereof, the external screw and the internal screw being configured to be brought into threaded engagement with each other, wherein
• a projection is formed at an upper end edge of the side wall of the stopper body so as to project outward from the side wall of the stopper body,
• a disc-shaped flange is formed at a lower end of the side wall of the stopper body so as to extend outward from a lower end edge of the side wall of the stopper body,
• the external screw is formed in a range along a screw axis direction from a connection position at which the side wall of the stopper body is connected to the flange to a distance that is not less than ⅓ of a distance between the connection position and the upper end edge and not greater than ⅔ of the distance between the connection position and the upper end edge, and
• in a state where the cap is threadedly attached to the side wall of the stopper body, a top surface at the upper end of the side wall of the stopper body and an upper surface of the projection are in surface contact with an inner surface of the top surface of the cap over an entire circumference thereof, and an outer circumferential edge of the projection is in contact with the inner circumferential surface of the side wall of the cap.