A seat apparatus for a vehicle, includes a main support control means for moving a side support portion inwardly and outwardly by means of a driving portion depending on a road shape, a support control means for operating the side support portion on the basis of an electronic map data before the vehicle reaches a curve starting point, a distance calculating means for calculating distance between an intersection and the curve starting point on the basis of the electronic map data, the intersection and the curve starting point, a determining means for determining whether or not control of the support control means is executed on the basis of the calculated distance and electronic map data accuracy, a means for executing the control of the support control means on the basis of determination of the determining means, and a means for refraining the control of the support control means.