ENERGY STORAGE DEVICE

Provided is a technique to break a case properly when an internal pressure of the case reaches a predetermined pressure. A herein disclosed energy storage device includes a case that is made of a first metal, includes a metallic piece that is welded to the case and that is made of a second metal being different from the first metal, and includes an intermetallic compound of the first metal and the second metal, the intermetallic compound being provided on a welded part of the case and the metallic piece.