The present invention provides a GDI injector of a vehicle engine that can change the level of swirl motion and make it possible to increase engine output and fuel mileage, comprising a nozzle body having an opening along its longitudinal axis, a fuel inlet member, a cylindrically-shaped needle valve being centrally located within the opening of the nozzle body, and a swirl generator, the swirl generator comprising: an inner case having a cylindrically-shaped body and a plurality of equally and angularly spaced lobes, the inner case being coupled to the needle; an outer case having a cylindrically-shaped body and a plurality of equally and angularly spaced grooves, the outer case being fixedly attached to the nozzle body; and an inner case rotator.