The present invention provides a method and apparatus for appropriately calculating 3D volume of cerebral hemorrhage lesion. The present invention sets a ROI for normal cerebral parenchymal region and a ROI for cerebral hemorrhage lesion respectively for a plurality of continuous slice images obtained by imaging the head having cerebral hemorrhage onset with an X-ray CT device, determines a mean value of the CT values of pixels within the ROI of normal cerebral parenchymal region for each of a plurality of images, then determines an amount of shift of mean values of images based on the mean value of one image, adjusts the CT value of pixels in the ROI of cerebral hemorrhage lesion for each image by using the amount of shift for each image, specifies the maximum value of the adjusted CT value through a plurality of images, and then calculates the 3D volume of the cerebral hemorrhage lesion.