Some customers may notice that the driver's seat gradually moves downward by itself and needs to be re-adjusted after 3 or 4 days of driving. This concern may be caused when a load, which is applied to the seat during braking, exceeds a specified level and may impact the retaining mechanism of the seat lifter and cause the seat to move downward. To eliminate this concern, the rigidity of the retaining mechanism of the seat lifter has been increased.