A thin film inspecting apparatus is provided with a storage section (14), which selects at least two feature quantities from among spectral reflectance spectrum feature quantities which are influenced by film thickness fluctuation of at least a first transparent thin film or a second transparent thin film, and stores at least two feature quantity characteristics which associate each of the selected feature quantities with each of the film thickness of the first transparent thin film and that of the second transparent thin film; a light irradiating section (11), which irradiates a substrate (S) to be inspected with white light from the side of a transparent glass substrate; a light receiving section (12), which receives reflection light from the substrate (S); and a calculating section (15) which obtains an actual measurement value of each feature quantity stored in the storage section (14) from the spectral reflectance spectrum based on received reflection light, and the film thickness of the first transparent thin film and that of the second transparent thin film by using the obtained actual measurement values of the feature quantities and the feature quantity characteristics stored in the storage section (14).