PURPOSE: To quickly determine the film thickness of magnetic materials on both surfaces with just one measurement by irradiating primary radiation on a sample to be measured and measuring the fluorescent X-rays generated from the front and rear surfaces of the sample.

CONSTITUTION: The sample 4 is placed on a sample base 5 and the primary radiation is irradiated on the sample 4 in the stage of measuring the unknown sample. The fluorescent rays are generated from the magnetic material layers 13, 15 and are added. The added rays are detected by a radiation detector 7 and are inputted as X-ray intensity data to a CPU 11. The thickness X of the magnetic material layers 13, 15 is calculated by the equation and is displayed on a display part 12. The film thickness of the magnetic material layers 13, 15 is thus quickly measured with just one measurement.