An electricity storage device comprising: a first electrode including a first metal foil and a first active material layer formed by applying a first active material to the first metal foil, wherein the first electrode includes a first end portion and a second end portion located at an opposite side of the first end portion, the first end portion is free from the first active material and defines a first active material-free portion that exposes the first metal foil, and the first active material layer extends from a border of the first active material layer and the first active material-free portion to the second end portion; a first separator portion that covers a first surface of the first electrode; a second separator portion that covers a second surface of the first electrode located at an opposite side of the first surface in a thicknesswise direction; a second electrode including a second metal foil and a second active material layer formed by applying a second active material to the second metal foil, wherein the second electrode includes a third end portion corresponding to the first end portion and a fourth end portion corresponding to the second end portion, which is located at an opposite side of the third end portion, the third end portion is free from the second active material and defines a second active material-free portion that exposes the second metal foil, and the second active material layer extends from a border of the second active material layer and the second active material-free portion to the fourth end portion, wherein the first electrode, the second electrode, the first separator portion, and the second separator portion are overlapped in a layered manner to form an electrode assembly, characterized in that each of the first separator portion and the second separator portion includes a strong bonding portion and a weak bonding portion that bond the first separator portion and the second separator portion, and the strong bonding portion (81; 101, 102; 123, 131) has a bonding strength that is strong relative to that of the weak bonding portion, the strong bonding portion (81; 101, 102; 123, 131) is located in each of the first separator portion and the second separator portion at a section proximate to the first end portion and extends along the first end portion, and the weak bonding portion is located in each of the first separator portion and the second separator portion at a section proximate to the second end portion and extends along the second end portion. a first electrode including a first metal foil and a first active material layer formed by applying a first active material to the first metal foil, wherein the first electrode includes a first end portion and a second end portion located at an opposite side of the first end portion, the first end portion is free from the first active material and defines a first active material-free portion that exposes the first metal foil, and the first active material layer extends from a border of the first active material layer and the first active material-free portion to the second end portion; a first separator portion that covers a first surface of the first electrode; a second separator portion that covers a second surface of the first electrode located at an opposite side of the first surface in a thicknesswise direction; a second electrode including a second metal foil and a second active material layer formed by applying a second active material to the second metal foil, wherein the second electrode includes a third end portion corresponding to the first end portion and a fourth end portion corresponding to the second end portion, which is located at an opposite side of the third end portion, the third end portion is free from the second active material and defines a second active material-free portion that exposes the second metal foil, and the second active material layer extends from a border of the second active material layer and the second active material-free portion to the fourth end portion, wherein the first electrode, the second electrode, the first separator portion, and the second separator portion are overlapped in a layered manner to form an electrode assembly, characterized in that each of the first separator portion and the second separator portion includes a strong bonding portion and a weak bonding portion that bond the first separator portion and the second separator portion, and the strong bonding portion (81; 101, 102; 123, 131) has a bonding strength that is strong relative to that of the weak bonding portion, the strong bonding portion (81; 101, 102; 123, 131) is located in each of the first separator portion and the second separator portion at a section proximate to the first end portion and extends along the first end portion, and the weak bonding portion is located in each of the first separator portion and the second separator portion at a section proximate to the second end portion and extends along the second end portion.