Magnetic core and deflection yoke having the same

The present invention relates to magnetic cores and deflection yokes having adjusting coils, such as, convergence coils wound around the cores. A deflection yoke includes a bobbin having a cavity formed in the longitudinal direction of the bobbin, and an adjusting coil having a magnetic core on which a thread is cut. The core inserted into the cavity is slidable in the longitudinal direction of the bobbin. The core has a marker formed on only one of ends of the core in the longitudinal direction. The core has been inserted into the cavity from the one end formed with the marker or the other end. The marker is formed on only one of ends of the core before or after the thread is cut thereon.