We present the detailed study of the response function of X- ray CCD cameras (XIS; X-ray Imaging Spectrometer). A pulse height distribution for monochromatic X-rays show a low- energy tail component and several weak lines in addition to main peak corresponding to incident X-ray energy. We divided the response function into six components; main peak, sub peak, triangle component, constant component, Si escape, and Si line. Each of them represents different physical processes in the CCD. We did the data fitting, numerical calculations, and Monte Carlo simulations to study energy dependence of the shape and intensity of these components, and made the response function as a function of X-ray energy.