When generating a tomographic image using a measuring X-ray CT apparatus that is configured to emit X-rays while rotating a specimen that is arranged on a rotary table and reconstruct a projection image thereof to generate a tomographic image of the specimen, an amount of geometric error that is included in the projection image is obtained in advance and stored; the projection image is corrected using the stored amount of geometric error; and a tomographic image is reconstructed using the corrected projection image.