The present invention provides an X-ray CT apparatus for imaging an MD image having a better S/N. The X-ray CT apparatus for taking an image with one of two materials within a subject to be examined being fractionated, acquiring two sets of data corresponding to said two types of X-ray having different energy by scanning using said two types of X-ray, generating a first image based on the two sets of data with the pixel values made by weighted addition of two types of CT values corresponding to the two types of X-ray, generating a second image based on the two sets of data, wherein the other one of the two types of material being fractionated, and generating an image by weighted subtraction of the first image and the second image.