An automatic steering system for a work vehicle includes: a steering travel apparatus for performing leftward turning based on a leftward steering amount with respect to a straight-forward direction and performing rightward turning based on a rightward steering amount with respect to a neutral position; a subject vehicle location calculator for calculating a location of a subject vehicle; a locational shifting calculator for calculating locational shifting from the travel route and the location of the subject vehicle; a vehicle body direction calculator for calculating a vehicle body direction that indicates a direction of a vehicle body; a directional shifting calculator for calculating directional shifting from the travel route and the vehicle body direction; a steering amount calculator for calculating a first steering amount, which is a steering amount for correcting the locational shifting and the directional shifting, based on the locational shifting and the directional shifting; and a steering amount limiter for limiting the first steering amount based on a second steering amount, which is the steering amount at present.