Abstract: An air bag 12 is spread flatly. Along four lines “R” that extend radially outward, the air bag 12 is sandwiched and held by line part forming units. By using a first press pieces 44, a portion between the neighboring lines “R” is pressed toward the gas inlet opening to form a first gathering portion, and form a ear portion 52 along each line “R”. Then, each ear portion 52 is pressed by a second press piece 45 to form a second gathering portion 54 that is like a bellows. When a gas is introduced into the gas inlet opening 26, the second gathering portion 54 is quickly expanded and increase of internal pressure of the air bag can be controlled. In the folding process, there is no need of turning the air bag 12 and thus a production device can be made simple in construction.

Abstract: An air bag 12 is spread flatly. Along four lines “R” that extend radially outward, the air bag 12 is sandwiched and held by line part forming units. By using a first press pieces 44, a portion between the neighboring lines “R” is pressed toward the gas inlet opening to form a first gathering portion, and form a ear portion 52 along each line “R”. Then, each ear portion 52 is pressed by a second press piece 45 to form a second gathering portion 54 that is like a bellows. When a gas is introduced into the gas inlet opening 26, the second gathering portion 54 is quickly expanded and increase of internal pressure of the air bag can be controlled. In the folding process, there is no need of turning the air bag 12 and thus a production device can be made simple in construction.