Side airbag device

A side airbag device to be incorporated in a seat-side portion of a vehicle, said side airbag device comprising:

• an inflator;
• and
• an airbag including a bag that is inflatable and a separator that separates said bag into a first chamber and a second chamber, said separator extending above a top of said inflator,
• wherein:
• said first chamber includes a support inflation portion and a protection inflation portion, said support inflation portion being deployable in such a shape that said support inflation portion gradually broadens from its lower end portion toward its upper end portion along said seat-side portion, said protection inflation portion being deployable above said upper end portion of said support inflation portion,
• said inflator is disposed so as to supply a gas into said support inflation portion,
• said separator includes at least one gas distribution hole, and
• said second chamber is located below said first chamber,
• wherein a part of said support inflation portion is level with said inflator with respect to a direction in which the seat-side portion extends vertically.