1. An X-ray CT apparatus, comprising: an X-ray generating unit configured to generate X-rays; an X-ray detecting unit including a plurality of X-ray detectors, each configured to detect the X-rays which are generated from the X-ray generating unit and transmitted through an object; and an image generating unit configured to correct signals acquired by the X-ray detecting unit and reconstruct an image therefrom, wherein the X-rays directed to a first of the X-ray detectors spread at the X-ray detecting unit as cross talk, and the image generating unit is configured to: measure the X-rays directed to the first of the X-ray detectors with the first of the X-ray detectors and with a second and a third of the X-ray detectors which are positioned on both sides of the first of the X-ray detectors, correct sensitivity differences of the signals acquired by the X-ray detectors in accordance with the signals detected by the first, second, and third of the X-ray detectors, calculate a whole component of crosstalk correction from the sensitivity difference corrected signals, and calculate a cross talk correction quantity for each of the X-ray detectors from the sensitivity difference corrected signals, and calculate a locally attenuating component for each of the X-ray detectors as a difference between a respective cross talk correction quantity and the whole component of crosstalk correction, and wherein when crosstalk corrections of the plurality of the X-ray detectors are performed by the image generating unit, the image generating unit is configured to: perform a crosstalk correction of each locally attenuating component using the whole component of crosstalk correction, and then reconstruct the image while correcting the signals from the X-ray detectors using a correction quantity of the whole component of crosstalk correction.