There is provided an acquiring method of a projection image of a sample whose shape is uneven with respect to a rotation center, the method comprising the steps of setting the sample S0 at a position of the rotation center C0 provided between an X-ray source 116a and a detector 117, and acquiring the projection image of the sample S0 at each different rotation angle for each different magnification ratio over a rotation angle of 180° or more by rotating the sample S0 around the rotation center C0, and by relatively changing a separation distance between the X-ray source and the rotation center, or a separation distance between the rotation center and the detector in an optical axis direction according to the shape of the sample S0 and the rotation angle of the sample S0.