To perform Fourier transformation fast on parallel computers while holding transformation object data and conversion result data in the same data division format.

Linear data to be transformed are arranged in a rectangular parallelepiped shape and mapped into three-dimensional transformation object data, the rectangular parallelepiped is divided by a plane perpendicular to Z direction, and data of each plane are assigned to one processor, and respective processors perform Y-directional Fourier transformation for the three- dimensional transformation object data according to the allocation to obtain 1st transformation result data (56). The respective processors perform X- directional Fourier transformation for the 1st transformation result data to obtain 2nd transformation result data (57). The 2nd transformation result data are divided by a plane perpendicular to the Y axis, the data are rearranged between the processors according to the divisions (58), and the respective processors perform transformation similar to Z-directional transformation to obtain final three-dimensional Fourier transformation result data (59).