Abstract: An air bag device for a passenger seat includes an air bag 1 stored in a folded state, an inflator 3, a case 5 for enclosing and storing the inflator 3 in the rear portion thereof and the air bag 1 in the front portion thereof respectively, and a cover member 7 for covering the front surface opening of the case. The case 5 further includes an air bag opening 6 in the horizontal direction thereof. The front portion of the air bag 1 defines a zigzag folded portion Z consisting of a plurality of folds respectively erected upwardly at the middle portions thereof along the extension of the lower side surface of the case 5 and the zigzag folded portion Z is then rolled up, and, in this state, the air bag 1 is stored in the case 5. Thereby, the air bag device for a passenger seat can reduce the number of folds of an air bag, and allows the air bag to be set into a case efficiently, and allows the air bag to be unfolded effectively.