In an energy storage device including a positive electrode plate and a negative electrode plate that are insulated from each other with a separator interposed therebetween, and a non-aqueous electrolyte, the separator includes a base material layer and a coating layer that is disposed on at least one surface of the base material layer, and the separator has an air permeability of the base material layer of 25 (sec/100 cc) or greater and 250 (sec/100 cc) or less, a porosity of the base material layer of 45% or greater, an air permeability of an interface between the base material layer and the coating layer of 15 (sec/100 cc) or less, and an air permeability of the coating layer of 15 (sec/100 cc) or less.