To reduce the squeaking of a wheel brake and also prevent the excess wear of a friction pad and facilitate the processing of the slide surface of a disc rotor.

In a ventilated disc rotor 1 providing two discs 1a, 1b arranged in parallel at some intervals and a radial plural ribs 3(1)-3(n) for forming a space between both while continuing to these discs, radial plural grooves 4(n), 5(n) are installed on the back surfaces (non-friction surface) 1au, 1bu of two discs 1a, 1b and the natural frequency and vibration mode of the discs 1a, 1b are adjusted and a brake squeaking is restrained.