This air cell cushion has a pair of side air cells extending upwardly from the upper surface side of the base member at both end sides in the lateral direction of the base member. The side air cells have a larger front-rear direction size than in the lateral direction thereof. Also, each side air cell is configured to inflate outward in the lateral direction. By this, in a case in which the side air cells face the armrests of the wheel chair, when the side air cells are inflated outward in the lateral direction, the outer side surfaces of the side air cells abut against or become adjacent to the armrests.