Internal airbag device

1. An internal airbag device comprising:

an inflator;

an airbag housing mounted in a roof in a region between a front seat and a rear seat; and

an airbag received in the airbag housing to deploy downwards by gas supplied from the inflator,

wherein the airbag includes:

a horizontal airbag section supported by the roof when the gas is supplied therein in a deployment thereof; and

a vertical airbag section, an upper portion of which vertically extends from a rear end of the horizontal airbag section opposite the rear seat in a deployment thereof and receives gas from the rear end of the horizontal airbag section;

wherein the rear end of the horizontal airbag section is aligned toward the rear seat; and

wherein a rear outer portion of the vertical airbag section is connected to the roof by at least a tether in order to reinforce the strength of the deploying airbag.

2. The internal airbag device according to claim 1 , wherein the vertical airbag section is a substantially planar airbag member involving spacing between a driver's seat and a front passenger seat.

3. The internal airbag device according to claim 1 , wherein at least a vent hole is provided at a boundary region formed between the horizontal airbag section and the vertical airbag section.

4. The internal airbag device according to claim 1 , wherein a lower end portion of the vertical airbag section is bent in a predetermined direction.

5. The internal airbag device according to claim 1 , wherein the inflator is a dual-stage inflator.