A sealing method that uses an electrostatic energy storage welding machine which includes an energy storage section including a plurality of energy storage parts is provided. A method of sealing a liquid inlet port of a power storage device includes burring in advance a through-hole of the liquid sealing port to raise a hole edge of the through-hole into a form of a projection, wherein the liquid sealing port of the power storage device to be sealed with electrolyte contained therein corresponds to an object to be welded; placing a spherical body that is a lid body on the projection; and performing resistance welding between the projection and the spherical body to seal the liquid inlet port.