Soft X-ray response of the CCD camera (XIS, X-ray Imaging Spectrometer), wh
ich will be aboard the Astro-E satellite, was investigated for the monochro
matic;X-rays in the 0.25-2.2 keV. Detailed pulse-height distribution was ex
amined particularly for O-K line, where significant low-energy tail was fou
nd. With the aid of Monte Carlo simulation we found that the photons absorb
ed in the channel stop was responsible for the component.