In a camshaft adjuster having a 4/2-way valve which rotates with the camshaft and includes a hydraulic control valve with a hydraulic control spool or piston, which is actuated in a control cylinder against the force of a compression spring between two end stops by a magnet armature of an electromagnet which is fastened to a control casing, the electromagnet is a repelling proportional magnet, whose magnet armature is seated fixedly on an armature plunger whose free end face is in contact with the control spool or with a part fixedly connected to the latter for moving the control spool against the force of the compression spring to actuate the hydraulic control valve so as to control fluid admission to the camshaft adjuster, the working stroke of the electromagnet exceeding that of the control spool.