Side airbag device for vehicle

A side airbag device for a vehicle, comprising:

• an inflator that is provided at a vehicle seat and that, when a side collision of a vehicle is sensed or predicted, is operated and generates gas;
• and
• a side airbag that is provided at a side portion of a seat back of the vehicle seat, and that inflates and expands between a seated passenger and a vehicle body side portion due to gas that the inflator generates being supplied to an interior of the side airbag, and that, in an inflated and expanded state, is divided into a front side bag portion and a rear side bag portion that are lined-up in a vehicle longitudinal direction, and at which a forwardly extending portion, that is provided at an upper portion of the rear side bag portion, extends from a side of a shoulder portion of the seated passenger toward a vehicle front side and is disposed above the front side bag portion, and, due to a dimension in a vehicle transverse direction of the forwardly extending portion being set to be smaller than that of the front side bag portion, a vehicle transverse direction inner side surface at an upper end side of the front side bag portion is inclined or curved so as to rise up while heading toward a vehicle transverse direction outer side.