A flexible power storage unit is obtained. Projections whose ridgelines extend in a first direction are provided on the front and the back of the power storage unit and depressions whose valley lines extend in a second direction are provided on the sides of the power storage unit. The projections and depressions are provided such that the ridgelines of the projections or extended lines of the ridgelines intersect with the valley lines of the depressions or extended lines of the valley lines.