Knee protection airbag device

A knee protecting airbag device is described in which a folded airbag 540 is housed in a case 113C and arranged in front and below the knees of a seated passenger. When an inflating gas from an inflator is fed to the airbag 540, it is so expanded that it rises rearward of the vehicle from an opening in the case to protect the knees of the passenger. The airbag 540 having completed its inflation is constructed such that the film length of the whole periphery of the airbag positioned along the edge of the open end of the case is larger than the length L of the whole periphery of the edge of the opening of the case 113C. When the airbag is completely inflated, the airbag 540 is forcedly contacts the edge of the open end 118e of the case 113 C so as to form wrinkles in the inflated airbag which stabilize the airbag's position.