Vehicle comprising an occupant's leg protection system with a knee airbag

To provide a knee airbag to be inflated quickly from below upward without having to use a high-output inflator and an occupant's leg protection system including the knee airbag. A knee airbag 18 in an inflated state is thicker at the upper part than at the middle part of the vertical direction of the knee airbag 18, and substantially equal in thickness at the greater part of the middle part of the vertical direction except the vicinity of the lateral sides of the knee airbag 18 (Fig 1).