Vehicle occupant protecting device

1. A vehicle occupant protecting device comprising:

an airbag that is accommodated at an upper portion of a vehicle seat, that receives a supply of gas from an inflator and is inflated and expanded toward a seat front side, and that includes a front inflating portion, which is inflated at a seat front side with respect to a head portion of a vehicle occupant, and a pair of left and right lateral inflating portions, which are connected to the front inflating portion and are inflated at sides of the seat with respect to the head portion, the airbag being structured as an integral bag body that covers the head portion; and

reinforcing portions that extend in a seat vertical direction at an interior of a seatback, and that connect an upper portion and a lower portion of a seatback frame that structures a frame of the seatback,

wherein:

the seatback frame is structured to include a pair of side frames, which are disposed with an interval therebetween in a seat transverse direction and which extend in the seat vertical direction, and an under frame that connects lower end portions of the side frames together in the seat transverse direction,

lower portions of the reinforcing portions are connected to connected portions of the side frames and the under frame,

each of the side frames and the reinforcing portions is structured to include a bottom wall and a pair of side walls that extend-out from both end portions of the bottom wall, and

the inflator is disposed within a cross-section that is surrounded by the bottom wall and the pair of side walls at the side frame, or within a cross-section that is surrounded by the bottom wall and the pair of side walls at the reinforcing portion.

2. The vehicle occupant protecting device of claim 1 , wherein:

the inflator is disposed further toward a seat lower side than the airbag; and

a gas jetting port is provided at a seat upper side end portion of the inflator.

3. The vehicle occupant protecting device of claim 1 , wherein the reinforcing portion includes a substantially triangular portion at a lower portion of the seatback frame.

4. The vehicle occupant protecting device of claim 1 , wherein the reinforcing portion includes an intersection portion.

5. A vehicle occupant protecting device comprising:

an airbag that is accommodated at an upper portion of a vehicle seat, that receives a supply of gas from an inflator and is inflated and expanded toward a seat front side, and that includes a front inflating portion, which is inflated at a seat front side with respect to a head portion of a vehicle occupant, and a pair of left and right lateral inflating portions, which are connected to the front inflating portion and are inflated at sides of the seat with respect to the head portion, the airbag being structured as an integral bag body that covers the head portion; and

reinforcing portions that extend in a seat vertical direction at an interior of a seatback, and that connect an upper portion and a lower portion of a seatback frame that structures a frame of the seatback,

wherein:

the airbag is accommodated within a headrest;

headrest supports that support the headrest are provided at an upper portion of the seatback frame; and

upper end portions of the reinforcing portions are connected to the headrest supports.

6. The vehicle occupant protecting device of claim 5 , wherein the reinforcing portion includes a substantially triangular portion at a lower portion of the seatback frame.

7. The vehicle occupant protecting device of claim 5 , wherein the reinforcing portion includes an intersection portion.