Knee protection airbag device

A knee protection airbag device comprising

• an airbag which is folded and accommodated in an accommodation part located in front of and below a knee of a seated occupant and is expanded and inflated toward a upper rear side from the accommodation part and causes a knee receiving portion to be arranged in front of the knee of the occupant when inflation gas flows in, wherein:
• the airbag includes an outer peripheral wall which connects outer peripheral edges of an occupant side wall portion on an occupant side and a vehicle body side wall portion on a vehicle body side;
• as an expansion completed shape of the airbag, a mounting portion, which is an upstream portion at the time of inflow of the inflation gas, and which is attached to the accommodation part with a lateral width dimension capable of being accommodated in the accommodation part, is disposed on a lower side and the knee receiving portion having a width dimension that is wider on both left and right sides than the mounting portion is arranged on an upper side;
• when the air bag is accommodated, the occupant side wall portion and the vehicle body side wall portion are overlapped and expanded flatly and roll-folding is performed such that an upper edge side of the knee receiving portion side approaches a lower edge side of the mounting portion side, end side portions on left and right sides of the roll-folded roll folding portion are formed as folded portions which fold over a central portion near a center in a left-right direction of the roll folding portion, the folded portion is overlapped with the central portion of the roll folding portion to form a folding completed body, and the folding completed body is accommodated in the accommodation part;
• the folded portion on at least one side in the left-right direction in the folding completed body is folded over the central portion with at least two folds, and is disposed by joining a first overlapping portion from a first fold on the central portion side to a second fold and a tip side part connected to the first overlapping portion and extending to a tip side of the end side portion with a joining unit;
• and
• a joining strength of the joining unit is set so that the joining between the first overlapping portion and the tip side part is released when the inflation gas flows into the airbag, and when the fold of the first fold is canceled and the first overlapping portion deviates from a rear area of the central portion.