An automatic steering system for an agricultural vehicle having a current position detecting function, the automatic steering system being configured to cause the vehicle to transfer from a previous route (Ls) to a subsequent route (Ln) by turn travel, the automatic steering system comprising: a first steering control module configured to perform steering control for first turn travel on the vehicle to cause the vehicle to leave the previous route (Ls) and head for the subsequent route (Ln); a second steering control module configured to perform steering control for second turn travel on the vehicle to cause the vehicle to enter the subsequent route (Ln); a third steering control module configured to perform steering control for shift travel on the vehicle to cause the vehicle to shift from the first turn travel to the second turn travel; characterised in that the automatic steering system further comprises: a virtual turning circle calculation module configured to calculate a virtual turning circle to be used as a target route for the second turn travel; and a tangent calculation module configured to calculate, as a target route for the shift travel, a tangent extending from a vehicle body reference point (Pv) in the first turn travel to the virtual turning circle, wherein the tangent calculation module is further configured to set the tangent calculated, at a reference tangent when an angle (θ) between the tangent and a traveling direction of the vehicle is within a first predetermined angle (θt), and the third steering control module is further configured to perform the steering control with the reference tangent set at the target route for the shift travel. a first steering control module configured to perform steering control for first turn travel on the vehicle to cause the vehicle to leave the previous route (Ls) and head for the subsequent route (Ln); a second steering control module configured to perform steering control for second turn travel on the vehicle to cause the vehicle to enter the subsequent route (Ln); a third steering control module configured to perform steering control for shift travel on the vehicle to cause the vehicle to shift from the first turn travel to the second turn travel; characterised in that the automatic steering system further comprises: a virtual turning circle calculation module configured to calculate a virtual turning circle to be used as a target route for the second turn travel; and a tangent calculation module configured to calculate, as a target route for the shift travel, a tangent extending from a vehicle body reference point (Pv) in the first turn travel to the virtual turning circle, wherein a virtual turning circle calculation module configured to calculate a virtual turning circle to be used as a target route for the second turn travel; and a tangent calculation module configured to calculate, as a target route for the shift travel, a tangent extending from a vehicle body reference point (Pv) in the first turn travel to the virtual turning circle, wherein the tangent calculation module is further configured to set the tangent calculated, at a reference tangent when an angle (θ) between the tangent and a traveling direction of the vehicle is within a first predetermined angle (θt), and the third steering control module is further configured to perform the steering control with the reference tangent set at the target route for the shift travel.