A gusset bag of the present invention includes a pair of flat surface portions, a pair of side surface portions, a content storing portion which is formed of the pair of flat surface portions and the pair of side surface portions and stores contents therein, an upper content non-storing portion which is provided above the content storing portion and stores no contents therein, a mouth portion provided on one of the pair of flat surface portions, a storing portion upper seal portion which is provided above the mouth portion and partitions the content storing portion and the upper content non-storing portion, an upper cut that has a shape in which at least one portion of a periphery of a predetermined region of the upper content non-storing portion on the storing portion upper seal portion side is not cut and another portion of the periphery is cut, and is formed to penetrate the pair of flat surface portions, and a penetrating portion provided in the predetermined region.