A method for manufacturing an energy storage device according to one aspect of the present invention includes: housing, in a case, an electrode assembly in which a negative electrode and a positive electrode are stacked; housing an electrolyte solution in the case; housing a gas, soluble in the electrolyte solution, in the case after the electrolyte solution is housed in the case; and sealing the case in a state where the gas soluble in the electrolyte solution is housed in the case.