1. An X-ray CT apparatus, comprising: an X-ray generating unit configured to generate an X ray; an X-ray detecting unit including a plurality of X-ray detectors, each configured to detect the X ray generated from the X-ray generating unit and transmitted through an object; and an image generating unit configured to correct a signal acquired by the X-ray detecting unit and reconstruct an image, wherein while crosstalk correction of a plurality of the X-ray detectors is performed at the image generating unit, correction of a locally attenuating component is previously performed and correction of a whole component of crosstalk is performed when the image is reconstructed.