To provide a phase contrast picture reflecting a precise phase difference, even if the phase difference exceeds 2π, in multiple radiation pictures obtained by a phase contract radiographing method.

A long-wavelength X-ray 12L transmitting through an object 21 is irradiated on a detection panel 31, while moving the detection panel 31 to obtain picture data SLn expressing X-ray pictures of the object in multiple radiographing positions. Similarly, picture data SSn are obtained using a short- wavelength X-ray 12S. A phase difference calculation means 41 calculates a phase difference caused by the both long-/short-wavelength X-rays' 12L and 12S transmitting the object 21 based on the respective picture data Son and Sn, and a true phase difference is obtained by correcting the phase difference of the long-wavelength X-ray 12L based on the respective phase differences so as to obtain picture data S1 expressing the phase contrast picture.