PURPOSE: To enable quantitative analysis for the composition and adhesion of a metallic film such as plated film of a fused Zn-Al plated steel plate especially being transferred accurately on line, by arranging a radiation source, a plurality of detectors, an arithmetic unit and the like.

CONSTITUTION: When X rays are made to irradiate a Zn-Al plated steel plate 1 at an angle of incidence of above 60°, fluorescence X rays are generated from the Zn-Al alloy film 1a and a steel plate 1b and X rays detectors 4 and 14 or the like are provided in the course thereof. Take off angles 2 and 3 and the like are above 10° to avoid a problem of only analyzing the surface layer of the film 1a. The fluorescence X rays detected by the detectors 4 and 14 or the like are converted to electrical signals therewith to be sent to amplifiers 5 and 15 or the like respectively and then, converted to the intensity of fluorescence X rays for a specified metal element with single-channel analyzers 6 and 16, scaler timers 7 and 17 and the like. Receiving a signal inputted from the detector 4, the timer 7 applies an output signal corresponding to the intensity of fluorescence X rays to an arithmetic unit 8, which 8 calculates the adhesion of the film 1a based on the input signal.