A variable valve timing device applied to an engine system may include a rotor supplied with oil and rotated in clockwise and counterclockwise directions, one-way clutches coupled to the rotor to limit an amount of rotation of the rotor, a sprocket having a rotor hole surrounding an external diameter portion of the rotor, a rotation shaft fitted into a shaft hole of the rotor for the supply of oil to oil grooves, and a shaft fixing member coupled to the rotation shaft to fix the rotor and the rotation shaft, wherein the one-way clutches restrict clockwise/counterclockwise rotation of the rotor by torque of a camshaft, achieving an improvement in fuel efficiency/emission material (EM) of an engine.