To provide an automatic steering system that can calculate an amount of positional deviation and an amount of azimuth deviation at high speed during a turning drive using a simple algorithm and can perform an accurate steering control.SOLUTION: An automatic steering system comprises: a reference point calculation unit for calculating a position of a reference point VP of a service vehicle 10； a positional-deviation-amount calculation unit for calculating a straight line that passes through the center P of a turning circle C and through the reference point VP as a reference straight line BL, and for calculating a distance from the point of intersection between the reference straight line BL and the turning circle to the reference point as an amount of positional deviation δ； an azimuth-deviation-amount calculation unit for calculating an azimuth of the vehicle, and for calculating an intersection angle θ between a line PL that is perpendicular to the reference straight line BL while passing through the reference point VP and the azimuth of the vehicle as an amount of azimuth deviation； and a steering control unit for outputting an amount of steering in which the amount of positional deviation δ and the amount of azimuth deviation θ are small.SELECTED DRAWING: Figure 7【課題】旋回走行において、簡単な算法で高速に位置ずれ量及び方位ずれ量を算出して、正確な操舵制御が可能な自動操舵システムの提供。【解決手段】自動操舵システムは、作業車１０における基準点ＶＰの位置を算出する基準点算出部と、旋回円Ｃの中心Ｐと基準点ＶＰとを通る直線を基準直線ＢＬとして算出し、基準直線ＢＬと旋回円との交点から前記基準点までの距離を位置ずれ量δとして算出する位置ずれ量算出部と、車体方位を算出し、基準点ＶＰを通り基準直線ＢＬに垂直な線ＰＬと車体方位との交差角θを方位ずれ量として算出する方位ずれ量算出部と、位置ずれ量δと方位ずれ量θとが小さくなる操舵量を出力する操舵制御部とを備える。【選択図】図７
