A gas pressure testing device for checking pressure of gas charged in a gas compartment portion of a bag in which the gas compartment portion is formed integrally therein and extends in a longitudinal direction in a sealed side edge portion of the bag, said gas pressure testing device being comprised of a measuring unit and a control unit, wherein said measuring unit is comprised of: a pressing member which is disposed on one side of a bag equipped with a gas compartment portion and suspended by being clamped at top portions of two lateral edges of the bag by a pair of grippers (11,12) and which is moved forward and backward in a thickness direction of the bag to press the gas compartment portion when moved forward, a receiving member which is disposed on another side of the bag and is positioned in a receiving position on a back side of the gas compartment portion, a support member which supports the pressing member on a rear side of the pressing member so as to move the pressing member in a forward-rearward direction while urging the pressing member forward, a drive source which moves the support member forward and rearward through a predetermined stroke, and a distance sensor which is provided on the rear side of the pressing member, is moved forward and backward together with the support member by the drive source, and measures a distance to the pressing member; and said distance sensor measures a distance between the distance sensor and the pressing member when the pressing member is moved forward by the support member moved forward by the drive source and sandwich the gas compartment portion between the pressing member and the receiving member which is positioned in the receiving position; wherein said control unit determines whether or not a pressure of gas that is filled in the gas compartment portion is within a preset range based on signals from the distance sensor; and wherein said support member is comprised of a moving member coupled to said drive source and an air cylinder installed on the moving member 43), said distance sensor is provided on the moving member, said pressing member is provided on a piston rod of the air cylinder, and the air cylinder is provided with a cylinder room which is installed on an opposite side from the piston rod and has therein compressed air under a predetermined pressure. a pressing member which is disposed on one side of a bag equipped with a gas compartment portion and suspended by being clamped at top portions of two lateral edges of the bag by a pair of grippers (11,12) and which is moved forward and backward in a thickness direction of the bag to press the gas compartment portion when moved forward, a receiving member which is disposed on another side of the bag and is positioned in a receiving position on a back side of the gas compartment portion, a support member which supports the pressing member on a rear side of the pressing member so as to move the pressing member in a forward-rearward direction while urging the pressing member forward, a drive source which moves the support member forward and rearward through a predetermined stroke, and a distance sensor which is provided on the rear side of the pressing member, is moved forward and backward together with the support member by the drive source, and measures a distance to the pressing member; and said distance sensor measures a distance between the distance sensor and the pressing member when the pressing member is moved forward by the support member moved forward by the drive source and sandwich the gas compartment portion between the pressing member and the receiving member which is positioned in the receiving position; wherein said control unit determines whether or not a pressure of gas that is filled in the gas compartment portion is within a preset range based on signals from the distance sensor; and wherein said support member is comprised of a moving member coupled to said drive source and an air cylinder installed on the moving member 43), said distance sensor is provided on the moving member, said pressing member is provided on a piston rod of the air cylinder, and the air cylinder is provided with a cylinder room which is installed on an opposite side from the piston rod and has therein compressed air under a predetermined pressure.