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 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 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 . <EOS>