A method for charging a bag equipped with a gas compartment portion with gas, wherein said method is for a bag formed integrally therein with a gas compartment portion extending in a longitudinal direction in a sealed side edge portion of the bag and having a gas inlet that is formed in a film sheet constituting a gas introduction section of the gas compartment portion and places an exterior of the bag in communication with an interior of the gas compartment portion, and said method is comprised of the steps of: aligning discharge outlets of gas injection nozzles, connected to a pressurized gas supply source, with the gas introduction section, injecting gas from the gas injection nozzles into the gas compartment portion through the gas inlet, and while the injection is in progress, cramping a blockage region, configured in the vicinity of the gas introduction section, on both sides of the bag with a gas blocking gripper to thereby block fluid communication of gas between the gas introduction section and the gas compartment portion, and then while maintaining the blocked state, pressure-holding the bag in the gas introduction section or a location in a vicinity thereof from both sides of the bag with hot plates to seal the gas introduction section or a vicinity thereof and encapsulate gas in the gas compartment portion, and wherein a pair of gas injection nozzles (23, 24) are disposed on both sides of the bag so as to reciprocate between a standby position thereof and an advanced position thereof, respectively, and the discharge outlets of the pair of gas injection nozzles are aligned, in the advanced position, with the gas introduction section from both sides, the method is for a bag equipped with a gas compartment portion and having gas inlets formed in film sheets of both sides of the gas introduction section, inside diameters of the discharge outlets (23a, 24a) of the gas injection nozzles are set to be smaller than a diameter or width of the gas introduction section, the discharge outlets of the gas injection nozzles are positioned to face each other with a predetermined gap therebetween that is, when the gas injection nozzles arrive at the advanced position, larger than a thickness of the gas introduction section, and the film sheets on both sides of the gas introduction section, expanded in the gap as a result of gas injection thereinto, closely adhere to the discharge outlets of the gas injection nozzles. said method is for a bag formed integrally therein with a gas compartment portion extending in a longitudinal direction in a sealed side edge portion of the bag and having a gas inlet that is formed in a film sheet constituting a gas introduction section of the gas compartment portion and places an exterior of the bag in communication with an interior of the gas compartment portion, and said method is comprised of the steps of: aligning discharge outlets of gas injection nozzles, connected to a pressurized gas supply source, with the gas introduction section, injecting gas from the gas injection nozzles into the gas compartment portion through the gas inlet, and while the injection is in progress, cramping a blockage region, configured in the vicinity of the gas introduction section, on both sides of the bag with a gas blocking gripper to thereby block fluid communication of gas between the gas introduction section and the gas compartment portion, and then while maintaining the blocked state, pressure-holding the bag in the gas introduction section or a location in a vicinity thereof from both sides of the bag with hot plates to seal the gas introduction section or a vicinity thereof and encapsulate gas in the gas compartment portion, and aligning discharge outlets of gas injection nozzles, connected to a pressurized gas supply source, with the gas introduction section, injecting gas from the gas injection nozzles into the gas compartment portion through the gas inlet, and while the injection is in progress, cramping a blockage region, configured in the vicinity of the gas introduction section, on both sides of the bag with a gas blocking gripper to thereby block fluid communication of gas between the gas introduction section and the gas compartment portion, and then while maintaining the blocked state, pressure-holding the bag in the gas introduction section or a location in a vicinity thereof from both sides of the bag with hot plates to seal the gas introduction section or a vicinity thereof and encapsulate gas in the gas compartment portion, and a pair of gas injection nozzles (23, 24) are disposed on both sides of the bag so as to reciprocate between a standby position thereof and an advanced position thereof, respectively, and the discharge outlets of the pair of gas injection nozzles are aligned, in the advanced position, with the gas introduction section from both sides, the method is for a bag equipped with a gas compartment portion and having gas inlets formed in film sheets of both sides of the gas introduction section, inside diameters of the discharge outlets (23a, 24a) of the gas injection nozzles are set to be smaller than a diameter or width of the gas introduction section, the discharge outlets of the gas injection nozzles are positioned to face each other with a predetermined gap therebetween that is, when the gas injection nozzles arrive at the advanced position, larger than a thickness of the gas introduction section, and the film sheets on both sides of the gas introduction section, expanded in the gap as a result of gas injection thereinto, closely adhere to the discharge outlets of the gas injection nozzles.