If an inspection method for inspecting a patterned medium is intended for the nanoimprint process control, it is necessary to measure a correct shape of each pattern element. On the other hand, if the inspection method is intended for the quality control of products, it is necessary to inspect the products on a I00 percent basis. However, the conventional method which uses SEM or AFM could not satisfy these requirements. According to the present invention, IO0-percent inspection of products becomes possible by a method including the steps of: irradiating a surface of a hard disk medium, on which a magnetic material pattern is formed, with a light beam including a plurality of wavelengths; detecting the intensity of a reflected light beam from the hard disk medium on a wavelength basis; calculating a spectral reflectance from the detected intensity of the reflected light beam; and detecting a shape of each pattern element formed on the hard disk medium on the basis of the calculated spectral reflectance.