PROBLEM TO BE SOLVED: To provide an apparatus configuration capable of more easily calculating a fat content inside an organ such as the liver.SOLUTION: On the inner surface of a lid 72 of a container body 70 housing a small animal 84 which is a subject, a fat phantom 73A and a muscle phantom 73B are mounted. The small animal 84 is positioned so that the position of the liver may be matched with the position of the fat phantom 73A and the muscle phantom 73B and is housed inside the container body 70. Then, the container body 70 is set to an X-ray CT apparatus, and a CT image of a cross section including the fat phantom 73A, the muscle phantom 73B and the liver is taken. The CT values of fat and muscles are respectively determined as reference values from the image of the fat phantom 73A and the muscle phantom 73B in the CT image, and the fat content of the liver is calculated from the relation between the reference values and the CT value of a liver part in the CT image.
