In a camshaft adjuster including a camshaft driven by a crankshaft of an internal combustion engine via an adjustable drive mounted on the camshaft by a mounting screw having a hollow shank with an axially movable control piston disposed in the hollow shank and an electromagnetic device for operating the control piston, the control piston is axially movable by the electromagnetic device for controlling the supply of oil to, and its release from, the camshaft adjuster for controlling the relative angular position of the crankshaft and the camshaft, the electromagnetic device operated piston also forming an oil pump for providing a supply of oil to the camshaft adjuster.