A turning center line is provided at a front edge side of a lid mounted on an upper surface of an instrument panel for permitting spreading of an air bag, and the lid is provided at a rear edge side thereof with a free end which is adapted to abut against a front windshield when the lid is opened. By contructing the lid-turning center line to be substantially parallel to the widthwise line of the front windshield, and the free end of the lid to be, in its closed position, substantially parallel to a line extending in a widthwise direction of the vehicle, or by constructing the lid-turning center line to be substantially parallel to the line extending in the widthwise direction of the vehicle, and the free end of the lid to be, in its closed position, substantially symmetrical to the widthwise line of the front windshield with respect to the lid-turning central line, it is ensured that the free end of the lid is permitted to abut against the front windshield substantially concurrently over the widthwise entire length. This avoids application of a localized load to the lid, thereby preventing any deformation or breaking of the lid.