PURPOSE: To improve an initial restrainability for an occupant on a vehicle, by providing an air bag means for moving a knee protector in the direction apart from the lower cover at a stage when collision is detected.

CONSTITUTION: When the upper half of the body of an occupant 50 on a vehicle is restrained by an air bag device 4 and a seat belt device, etc., at the time of the collision of an automobile, the lower half of the body, a knee part in particular, of the occupant 50 on the vehicle is about to be moved forward due to reaction. At that time, the knee protector 3 of a knee protector device 1 is moved rearward in the automobile sooner than the movement of the occupant 50 on the vehicle, improving the initial restrainability of the knee part 50b. Concurrently in usual, large gap is ensured between a seat position and the knee protector 3 of a lower cover 2. Consequently, freedom for layout is ensured to secure a gap, without detracting boarding and alighting property, between a mean knee position for the occupant on the vehicle and a lower cover 2.