An energy storage cell includes an energy storage part for storing electric charges, a container for housing the energy storage part, and a pair of electrode terminals connected to the energy storage part and exposed to the outside of the container. The container is formed to have a thick polygonal outer shape and a groove part linearly extending in a direction perpendicular to a thickness direction is provided in each of a pair of mutually facing side surfaces of the polygonal shape. Each of the electrode terminals includes a base end part connected to a corresponding polarity of the energy storage part in the container and an exposed part exposed to the outside of the container, and the exposed part is formed along an inner side of the groove part.