An improved synthetic resin spout stopper to be combined with a discharge port of a container is provided. The spout stopper does not pose difficulty in breaking an annular score formed in an annular flange wall, when discarding the container. Damage to the annular score is avoided even if a considerably great impact is applied to the spout stopper owing to a fall of the container. Damage to the annular score is also avoided even when ultrasonic welding is adopted for welding the container and the spout stopper together. In an inner peripheral edge part of the annular flange wall, an annular additional score is disposed adjacent to the annular score radially outwardly of and/or radially inwardly of the annular score.