Energy storage device

An energy storage device, comprising:

• a casing having an opening;
• an energy storage element housed in the casing;
• a lid plate mounted in the opening of the casing;
• a terminal member integrally fixed to, and insulated from, the lid plate by an insulating synthetic resin;
• and
• a current collector configured to electrically connect the energy storage element and the terminal members to each other,
• wherein the terminal member includes:
• a metal-made reverse film which is deformed when a pressure in the casing is increased;
• and
• an external connecting portion electrically connected to an external circuit,
• wherein the current collector includes a breakable portion configured to be broken due to a deformation of the metal-made reverse film,
• wherein a thickness of the external connecting portion is set larger than a thickness of the metal-made reverse film in a reversing direction in which the metal-made reverse film is reversed due to the deformation of the metal-made reverse film, and
• wherein the metal-made reverse film projects downward, in a direction opposite to a direction that the terminal member projects from the lid plate, from a bottom surface of the external connecting portion.