A liquid blow molding method of molding a synthetic resin preform having a mouth portion into a liquid container of a predetermined shape, the method including: an air-liquid replacement step of exhausting the air inside the preform to the outside while a liquid is supplied into the preform from the mouth portion through a blow nozzle; an air-liquid separation step of separating the air from the liquid inside the preform by rotating the preform about an axial center of the mouth portion; and a blow molding step of molding the preform into a container of a predetermined shape by supplying a pressurized liquid into the preform from the mouth portion through the blow nozzle, after the air-liquid separation step.