ELECTRICITY STORAGE DEVICE AND INSULATING HOLDER

An electricity storage device includes: an electrode body including at least one positive electrode plate, at least one negative electrode plate, and a separator. an insulating holder that is formed by folding a sheet made of an insulating material and accommodates therein the electrode body; an outer case which has an opening and accommodates therein the electrode body with the insulating holder and an electrolyte; and a sealing plate. The outer case has a bottom plate part and a plurality of side walls standing from the bottom plate part, and the opening is formed in a position to face the bottom plate part. The insulating holder has a plurality of side surface parts respectively facing the plurality of side walls, and a bottom surface part that faces the bottom plate part. At least one of the side surface parts or the bottom surface part has a bellow-folded structure.