An energy storage apparatus includes: an energy storage device including a flat electrode assembly in which electrodes are layered and a prismatic case in which the electrode assembly is housed; and a spacer arranged adjacently to the energy storage device in a first direction, wherein the spacer is formed such that a thickness size in the first direction of a center portion of the spacer in a second direction, which is a direction orthogonal to the first direction and is a direction parallel to a surface of the spacer that faces the energy storage device, is set larger than a thickness size in the first direction of other portions of the spacer arranged adjacently to the center portion of the spacer in the second direction, and a width of the center portion of the spacer in a third direction orthogonal to the first and second directions at a contact portion of the spacer with the energy storage device is set smaller than a width of the case in the third direction.