A magnetic bolt has a movable and electromagnetically operable locking member which, in conjunction with a locking part arranged on the rotor of a lock cylinder, blocks or releases the rotor, independently of the mechanical tumblers depending on whether the locking member is located in a free-running slot or a locking notch of the locking part. The magnetic bolt is arranged in a recess in the lock cylinder stator and provides an electromagnetic locking operation by energizing a field coil.