A disc rotor formed of flaky graphite cast iron in which the natural frequency of the disc rotor is set by the graphite length in the flaky graphite cast iron structure.For preventing resonant vibrations ascribable to the self-excited vibrations of the component parts of disc brakes, such as pads, the natural frequency of the disc rotor are shifted from the frequency of excited vibrations of the component parts of disc brakes, such as pads.