PURPOSE: To uniformly roughen the surface of the carbon substrate for a magnetic disk having a precision finished surface and to impart an excellent adsorption preventive property thereto by irradiating the above-mentioned carbon substrate with UV rays.

CONSTITUTION: The bonds, such as C-C and C=C, of carbon C constituting the carbon substrate for the magnetic disk are cut off by the energy of the UV rays and the free radicals of C are formed when the substrate surface is precision-finished and is irradiated with the UV rays. On the other hand, ozone O3 is generated when oxygen O2 is irradiated with UV rays of 184.9nm wavelength. This O3 is cracked by absorbing the UV rays of 253.7nm wavelength and generates atomic oxygen O. This O has a powerful oxidizing powder and forms the simple molecules of CO and CO2 by reacting with the C. The carbon substrate is the crystal structure of the assemblage of fine crystals of several 100. The gaseous molecules of the Co and C2 fly near to the grain boundaries thereof and the parts near the grain boundaries are recessed from the other parts, by which microruggedness is formed on the substrate surface. Then, the entire part of the substrate surface is roughened to uniform roughness.