SIDE AIRBAG DEVICE

A side airbag device is provided, in which gas does not directly act on a sewing portion forming a first end of an inner tube so that the first end is not damaged by the gas. The side airbag device includes: an airbag (2); an inflator (3) that supplies gas to the airbag (2); and an inner tube (4) formed of a fabric and provided so as to cover discharge holes (3a) of the inflator (3). The inner tube (4) is structured such that the inner tube (4) protrudes toward a center of the airbag (2) in a deployed state and that a first end (4b) that is in a direction, in which the gas is discharged from the inflator (3), is closed, and second ends (4c) that are in a vehicle height direction of the airbag (2) in the deployed state and intersecting the discharge direction of the gas, which is discharged from the discharge holes (3a) of the inflator (3), are open. The inner tube (4) is folded back at a folded-back portion (4d) inside the airbag (2) when the airbag (2) is folded in a case where the side airbag device is installed in a seat back (SB) of a vehicle seat.