A liquid container manufacturing method for manufacturing, from a synthetic resin preform, a liquid container containing a content liquid using a nozzle unit and a blow-molding mold, wherein the nozzle unit includes: a liquid supply path that is connected to a pressurized liquid supply source and that extends to a blow nozzle; and a flow path that extends from an opening provided on an inner circumferential surface of the blow nozzle to an interior of the nozzle unit and that is configured to be opened and closed by a valve (Va) embedded in the blow nozzle, and the flow path includes: a communication space adjacent to the opening; and a pin accommodating space which is adjacent to the communication space and in which a seal pin configured to make advancing and retracting movements along an axial direction is arranged, and wherein the seal pin has a protruding portion configured to enter the communication space in a closed state of the valve (Va), the liquid container manufacturing method comprising a liquid blow molding step of molding the preform into the liquid container having a shape conforming to an inner surface of the blow-molding mold, by supplying, through the liquid supply path to an interior of the preform, a pressurized liquid using the pressurized liquid supply source in a state in which the blow nozzle is engaged to a mouth of the preform. a liquid supply path that is connected to a pressurized liquid supply source and that extends to a blow nozzle; and a flow path that extends from an opening provided on an inner circumferential surface of the blow nozzle to an interior of the nozzle unit and that is configured to be opened and closed by a valve (Va) embedded in the blow nozzle, and the flow path includes: a communication space adjacent to the opening; and a pin accommodating space which is adjacent to the communication space and in which a seal pin configured to make advancing and retracting movements along an axial direction is arranged, and wherein the seal pin has a protruding portion configured to enter the communication space in a closed state of the valve (Va), the liquid container manufacturing method comprising a liquid blow molding step of molding the preform into the liquid container having a shape conforming to an inner surface of the blow-molding mold, by supplying, through the liquid supply path to an interior of the preform, a pressurized liquid using the pressurized liquid supply source in a state in which the blow nozzle is engaged to a mouth of the preform. a communication space adjacent to the opening; and a pin accommodating space which is adjacent to the communication space and in which a seal pin configured to make advancing and retracting movements along an axial direction is arranged, and wherein the seal pin has a protruding portion configured to enter the communication space in a closed state of the valve (Va), the liquid container manufacturing method comprising a liquid blow molding step of molding the preform into the liquid container having a shape conforming to an inner surface of the blow-molding mold, by supplying, through the liquid supply path to an interior of the preform, a pressurized liquid using the pressurized liquid supply source in a state in which the blow nozzle is engaged to a mouth of the preform.