Provided is a method for manufacturing an energy storage device. In the method of manufacturing an energy storage device, a lid assembly is formed by integrating a lid plate covering an opening of a case which houses a plate, an external terminal exposed to outside of the lid plate, and a conductive plate portion disposed inside the lid plate in an overlapping manner. The lid assembly is disposed between a vibrating jig and a receiving jig, a tab of the plate is disposed between the conductive plate portion and the vibrating jig, and ultrasonic welding is applied to the tab and the conductive plate portion.