An equivalent phantom is used for an X-ray Talbot imaging apparatus which includes an X-ray source, a plurality of gratings and an X-ray detector. The apparatus captures at least a Moire image from which a differential phase image of an object is generated. The equivalent phantom includes a first substance having a first refractive index and a second substance having a second refractive index. A ratio of the first refractive index to the second refractive index is equal to a ratio of a refractive index of a soft tissue to a refractive index of a surrounding tissue. At least a part of a shape of one of the first and second substances is equal to a shape of a corresponding portion of the soft tissue.
