To provide an energy dispersion type radiation detecting system and a method of measuring a content of an object element capable of carrying out a measurement by determining an intensity of an incidence radiation to constitute an optimum minimum limit of detection by restraining an influence of a pile up, the energy dispersion type radiation detecting system includes an incidence system of irradiating the incidence radiation to a sample by a predetermined intensity, a detection system of detecting a radiation emitted from the sample by irradiating the incidence radiation for specifying a content of an object element of the sample based on a spectrum of the detected radiation, and the energy dispersion type radiation detecting system includes a control portion capable of irradiating the incidence radiation by an optimum intensity by determining the optimum intensity of the incidence radiation minimizing a minimum limit of detection of the object element based on the spectrum of the detected radiation.