A power storage device comprising: an electricity storage element; a case housing the electricity storage element, the case having an opening; and a sealing member sealing the opening, wherein: the sealing member includes an elastic member fit in the opening, the elastic member contains an elastic polymer and a hindered phenol compound, the hindered phenol compound having a phenol skeleton includes a first hindered group and a second hindered group, the first hindered group being bonded to a first substitution site of the phenol skeleton, the second hindered group being bonded to a second substitution site of the phenol skeleton, each of the first substitution site and second substitution site being adjacent to a substitution site of the phenol skeleton to which a phenolic hydroxy group is bonded, the first hindered group and the second hindered group each include one or more tertiary carbon atoms, one of the one or more tertiary carbon atoms in the first hindered group is bonded to the first substitution site, one of the one or more tertiary carbon atoms in the second hindered group is bonded to the second substitution site, wherein the elastic member further includes talc, and characterized in that a content ratio of the talc included in the elastic member is more than or equal to 10 parts by mass and less than 100 parts by mass with respect to 100 parts by mass of the elastic polymer included in the elastic member. an electricity storage element; a case housing the electricity storage element, the case having an opening; and a sealing member sealing the opening, wherein: the sealing member includes an elastic member fit in the opening, the elastic member contains an elastic polymer and a hindered phenol compound, the hindered phenol compound having a phenol skeleton includes a first hindered group and a second hindered group, the first hindered group being bonded to a first substitution site of the phenol skeleton, the second hindered group being bonded to a second substitution site of the phenol skeleton, each of the first substitution site and second substitution site being adjacent to a substitution site of the phenol skeleton to which a phenolic hydroxy group is bonded, the first hindered group and the second hindered group each include one or more tertiary carbon atoms, one of the one or more tertiary carbon atoms in the first hindered group is bonded to the first substitution site, one of the one or more tertiary carbon atoms in the second hindered group is bonded to the second substitution site, wherein the elastic member further includes talc, and characterized in that a content ratio of the talc included in the elastic member is more than or equal to 10 parts by mass and less than 100 parts by mass with respect to 100 parts by mass of the elastic polymer included in the elastic member. the sealing member includes an elastic member fit in the opening, the elastic member contains an elastic polymer and a hindered phenol compound, the hindered phenol compound having a phenol skeleton includes a first hindered group and a second hindered group, the first hindered group being bonded to a first substitution site of the phenol skeleton, the second hindered group being bonded to a second substitution site of the phenol skeleton, each of the first substitution site and second substitution site being adjacent to a substitution site of the phenol skeleton to which a phenolic hydroxy group is bonded, the first hindered group and the second hindered group each include one or more tertiary carbon atoms, one of the one or more tertiary carbon atoms in the first hindered group is bonded to the first substitution site, one of the one or more tertiary carbon atoms in the second hindered group is bonded to the second substitution site, wherein the elastic member further includes talc, and characterized in that a content ratio of the talc included in the elastic member is more than or equal to 10 parts by mass and less than 100 parts by mass with respect to 100 parts by mass of the elastic polymer included in the elastic member.