In a knee protecting airbag device of the present invention, in the lower area inside a column cover, a case housing an airbag is attached to a steering column. The steering column includes a movable member for moving toward the front side of a vehicle along the axial direction of the column at the time when an impact on the front of the vehicle acts, and an unmoving stationary member, so that the column can absorb the impact when the movable member moves. The case is attached to such an area of the movable member that the case hits the stationary member when the moving member moves and absorbs impact, and the case can be deformed before or at the time of hitting the stationary member so that the moving stroke of the movable member is preserved when it moves.