Abstract: A variable intake- and/or exhaust-valve timing control system for an internal combustion engine comprises a cam sprocket having a driven connection with an engine crankshaft, a camshaft, a ring gear provided between the camshaft and the cam sprocket for adjusting a relative phase angle between the cam sprocket and the camshaft, and a ring gear drive mechanism for drivingly controlling the ring gear via fluid pressure created by an engine oil pump, depending upon the operating state of the engine. The drive mechanism includes a subsidiary oil pump for supplying a fluid pressure greater than a designated pressure level to the ring gear, during low engine speed and high engine load.