1. A concentration measuring method for measuring a concentration of an object component in a sample from a fluorescent X-ray intensity by means of a fluorescent X-ray spectrometer, comprising steps of: irradiating the sample with primary X-rays; acquiring a spectrum of secondary X-rays generated from the sample; obtaining a fluorescent X-ray intensity of the object component included in the sample from the acquired spectrum; subtracting a background, which is related to scattered X-rays included in the secondary X-rays and a signal specific to the fluorescent X-ray spectrometer, from the obtained fluorescent X-ray intensity of the object component; performing a correction corresponding to a composition of the sample for the fluorescent X-ray intensity obtained by subtracting the background; and calculating a concentration of the object component in the sample on the basis of a calibration curve representing a relation between a concentration of the object component and a value obtained after performing the correction for the fluorescent X-ray intensity obtained by subtracting the background.