PURPOSE: To start editing even when not all subset data are gathered, to reduce wasteful waiting time and to complete editing in short time as possible.

CONSTITUTION: An actual document space area and a virtual space area 41 are provided in a storage device. Virtual editing is performed by arranging respective subset frames GF for plural subset in order. In performing the virtual editing, the start position of the subset frame GF to be arranged in second order is designated with the relative position with respect to the procedingly arranged subset frame GF, one or plural subset frame GF is cut out from a cirtual editing space 51 which is a virtually edited cirtual space area 41 by a cutting frame CF corresponding to the actual document space area, and the cut-out subset frame GF is arranged in the actual document space area.