Abstract: An apparatus for and a method of measuring at least one painted layer formed on a sample to be analyzed, which sample may be, for example, a galvanized steel including a substrate having the painted layer formed thereon with or without an intervention of a primer coated layer. In the practice of the invention, radiation is directed onto a surface of the painted layer so as to excite the sample. The intensity of resultant Compton scattering rays, the intensity of resultant fluorescent X-rays emitted from zinc contained in a plated zinc and the intensity of resultant fluorescent X-rays emitted from strontium contained in the primer coated layer are measured, and also the absorption of the fluorescent X-rays are taken into consideration, to provide a basis for calculation of the amount of paint coating forming the painted layer. In this way, the amount of primer and paint material both applied to the galvanized steel can be easily measured on a non-destructive basis.