Automatic steering system for working vehicle

An automatic steering system for a working vehicle, for automatic maneuvering of the working vehicle running on a working ground surface along a desired running path, in which the influences of various ground surface environments and of any aging degradation and/or individual variation of the working vehicle may be minimized, and the automatic steering operation may be conducted with improved stability. The automatic steering system includes a measurement section for acquiring measurements including those of the position, velocity, heading direction, and attitude of the vehicle and a data processing section. The data processing section includes a vehicle related parameter estimator for determining a value of a vehicle related parameter and a ground surface related parameter estimator for determining a value of a ground surface related parameter.