A method of manufacturing a liquid container, in which, a nozzle unit includes a blow nozzle having a supply port and a spare supply tube having, at a lower end thereof, a spare supply port. The method includes: an air exhausting step of exhausting the air in the preform to the outside by supplying a liquid into the preform from the spare supply port located at a bottom portion of the preform; a liquid blow molding step of molding the preform into a liquid container by supplying a pressurized liquid from the supply port into the preform; and a headspace forming step of forming a headspace by exhausting the liquid from the inside of the liquid container.