Occupant protection device

1. An occupant protection device which protects an occupant seated in a seat, comprising:

a seat belt; and

an airbag which is arranged in an area of a lap belt in the seat belt which restrains a waist of the occupant when worn and inflates so as to cover a front side of the occupant when operated, wherein:

the airbag includes a bag body which inflates so that inflation gas flows into the inside when operated and projects forward and upward and a regulatory tether which regulates a position of the bag body when inflation is completed;

a thigh abutment surface capable of abutting on a thigh of the occupant is arranged on a lower surface side of the bag body when the inflation is completed and an upper body restraining surface capable of restraining an upper body of the occupant is arranged on a rear surface side when the inflation is completed; and

the regulatory tethers are arranged on both left and right sides of the bag body when the inflation is completed and each of the regulatory tethers connects a base end to a side surface side of the bag body when the inflation is completed and connects a tip to a side surface side of the seat arranged rearward and downward from the base end.

2. The occupant protection device according to claim 1 , wherein

the regulatory tethers are configured to respectively connect the base ends to left and right side surface sides of the bag body in a region on an upper side of the upper body restraining surface.

3. The occupant protection device according to claim 2 , wherein

the bag body has a substantially triangular prism shape in which an axial direction is substantially along a left-right direction as an outer shape when inflation is completed and is configured to include a front wall portion, which is arranged on a front side away from the occupant when the inflation is completed, a rear upper wall portion and a rear lower wall portion arranged on the occupant side when the inflation is completed, and a left wall portion and a right wall portion, which are arranged so as to face each other on a left-right direction side when the inflation is completed,

the upper body restraining surface is composed of the rear upper wall portion,

the thigh abutment surface is composed of the rear lower wall portion,

the bag body is configured to be formed by binding peripheral edges of two base materials, an occupant side panel and a front side panel, to each other,

the occupant side panel is configured to include,

an upper part forming the rear upper wall portion and regions on rear upper sides in the left wall portion and the right wall portion, and

a lower part forming the rear lower wall portion and regions on rear lower sides in the left wall portion and the right wall portion,

the front side panel forms the front wall portion and regions on front sides in the left wall portion and the right wall portion, and

the regulatory tether is configured to bind the base end to a region of a binding part which binds peripheral edges of the front side panel and the upper part.

4. The occupant protection device according to claim 1 , wherein:

the airbag includes a rear tether which is located on a rear surface side of the bag body; and

the rear tether connects a base end to a rear surface side of an upper-lower intermediate portion of the bag body when the inflation is completed and connects a tip extending downward from the base end to the lap belt side and a length dimension is set a dimension in which a connecting portion connecting the base end of the bag body can be pulled toward the lap belt side.