X-ray CT can acquire high quality tomograms and can be used for various diagnoses including early detection of cancers. Utilizing the energy information of X-rays as the energy subtraction method is useful to improve the image contrast because each material has different energy dependences on interactions with X-ray. To utilize the energy information of X-rays, we attempt to use the filtered X-rays as X-ray sources with different energy spectra. Especially we propose utilizing a comb-shape filter placed between an X-ray source and an object to simultaneously acquire transmission images by filtered and unfiltered X-rays. In this paper, we study the feasibility of the proposed CT technique through simulations and basic experiments. The transmission images through a comb-shape filter have a striped structure. By estimating the X-ray intensities at intermediate points of discrete data points with the interpolation method, we can simultaneously acquire two transmission images obtained by filtered and unfiltered X-rays. From basic experiments imitating a comb-shape filter, we confirmed that the contrast of the images can be improved by applying the energy subtraction method using comb-shape filtered X-rays. In addition, we considered the spacing of a comb-shape filter through basic experiments.