In the airbag device of the present invention, a cylinder-shaped inflator includes a discharge side end portion having a plurality of gas discharge ports. The discharge side end is connected with the airbag utilizing a clamp by being inserted into a tubular gas inlet port of the airbag. Each of gas discharge ports includes a circumferential opening and an end face opening. The end face opening emits inflation gas in an axial direction of the inflator when the inflator is connected with the gas inlet port. Between each of the circumferential openings is a supporting plane for supporting an inner surface of the gas inlet port. The discharge side end includes a guide portion for redirecting inflation gas flowing from inside to directions perpendicular to the axis of the inflator when the gas inlet port is not connected with the inflator, such that inflation gas is discharged from the circumferential openings of the gas discharge ports. The airbag of the present invention dispenses with a diffuser and facilitates a connecting work of a cylinder-shaped inflator and an airbag.