A liquid-containing container manufacturing method includes: a liquid blow molding step of molding a preform into a liquid-containing container of a shape along an inner surface of a mold for blow molding, by supplying a liquid pressurized from a supply path into the preform in a state in which a blow nozzle engages with a mouth part of the preform; and a headspace formation step of forming a headspace in the liquid-containing container, by operating a pressurized liquid supply source in a suction direction to discharge the liquid from inside the liquid-containing container through the supply path, thereafter closing the supply path, and discharging the liquid from inside the liquid-containing container through a discharge port of a discharge rod extending into the liquid-containing container through the blow nozzle.