A head protecting airbag device is adapted to be mounted on a vehicle provided with an assist grip that is mounted on an upper edge of a window by front and rear attachment portions. An airbag includes a gas inflow portion which is inflatable with an inflation gas and a non-inflow portion which admits no inflation gas. The gas inflow portion includes a shielding portion which covers an area of the window below the assist grip. The non-inflow portion includes a thickness regulating portion which regulates the thickness of the shielding portion when the airbag is inflated. In the shielding portion, the thickness regulating portion is disposed on a front upper portion of the shielding portion below the front attachment portion of the assist grip, and is not disposed below the rear attachment portion of the assist grip.