Assuming that the s-polarized light of the incident light is reflected from the interface of the layer B, and the p-polarized light is reflected from the interface of the layer D, each amplitude reflectivity of Rs and Rp are calculated, and tan of a function of the amplitude ratio of the p-polarization component to the s-polarization component and cos of a function of the phase difference between the p-polarization component and the s-polarization component are calculated, thereby creating reference data. The thickness tA of the oxide film 301 is determined on the basis of the reference data. Thus, the thickness and cross section shape of the film formed on the multilayer interconnection are measured in a nondestructive manner with high throughput.