PURPOSE: To provide an evaluation method for carbon protective film capable of simultaneously measuring and evaluating the thickness and quality of the carbon protective film of a magnetic recording medium.

CONSTITUTION: In an evaluation method for carbon protective film of a magnetic recording medium which is formed by laminating at least a non-magnetic bed film 3, a magnetic film 4, and a carbon protective film 5 on a substrate 2, an apparent optical constant of a laminated structure is determined by ellipsometric method with the laminated structures 2, 3, and 4 under the carbon protective film 5 used as optical bed. Next the optical constants (refractive index and absorption coefficient) and film thickness are obtained using the apparent optical constant by ellipsometric method with the carbon protective film 5 used as optical thin film. The refractive index corresponds accurately with the hydrogen content rate of the carbon protective film enough to become a film quality decision factor. Then the quality and thickness of the film can be measured and evaluated simultaneously by an ellipsometer.