An object is to reduce the influence of chlorine in plastics when the metal concentrations in the plastics are analyzed. In an X-ray analyzer including an X-ray generating part for irradiating primary X-rays onto a sample and an X-ray detector for detecting an X-ray from the sample, primary X-rays is irradiated onto a plastic sample from the X-ray generating part, the X-ray intensity of chlorine is obtained from the plastic sample by the X-ray detector, and the scattered X-ray intensity where the primary X-ray has been scattered by the plastic sample is obtained by the X-ray detector. A chlorine X-ray intensity ratio calculating means for dividing the X-ray intensity of chlorine by the scattered X-ray intensity to calculate a chlorine X-ray intensity ratio is provided. The calculated chlorine X-ray intensity ratio and the chlorine concentration in the plastic sample have positive correlation each other. A relative chlorine concentration calculating means adapted to calculate the relative chlorine concentration in the plastic sample from the chlorine X-ray intensity ratio is provided.