Aging of farmers and shortage of agricultural workforce have necessitated the development of agricultural automation in the world. Many automatic vehicle guidance researches have been done, however, most of them are related to navigating a wheel-type farm mobile robot along rectilinear paths. This paper proposes an automatic tractor guidance system that enables the tractor to run autonomously along the curved path on meadow. First, a curved path was given in the form of a plane figure. Four-dimension state-vector space was reconstructed from a given path using kinematics vehicle equation. Second, linearization for vehicle equations was performed in the neighborhood of "future points", as defined in preview control theory. Then linear quadratic(LQ) method was utilized to design the on-tracking controller. Finally, field tests were conducted with the proto type tractor equipped with the developed controller. The travel speed was set at 1.5 m/s. Results indicated that the maximum deviations were 35 cm when the tractor follows sinusoidal path and circular paths.