A liquid blow molding method comprises: a preliminary pressurization step of operating a pressurization supply source (30) in a state in which a blow nozzle (23) is closed by a seal body (27), to preliminarily pressurize a liquid (L) between the pressurization supply source (30) and the blow nozzle (23); an operating condition setting step of setting an operating condition of the pressurization supply source (30) based on data obtained as a result of the preliminary pressurization step; and a blow molding step of operating the pressurization supply source (30) under the operating condition set in the operating condition setting step in a state in which the blow nozzle (23) is opened, to liquid blow mold a preform (2) into a container of a predetermined shape.