To quickly prepare a raster image even from data described in a page-description language which is not page-independent.

This image data generation device is provided with: a page division part 10 for dividing data described in the page-description language by page units; a plurality of RIPs 40 for preparing raster data from the divided data; and an RIP control part 50 for assigning pages for preparing raster data to each RIP 40, and for controlling each RIP 40 to execute the development registration of print resources in each page accompanied with at least a change in print resources regardless of the assignment of the pages. The RIP control part 50 transmits the data of each of the divided pages to each RIP 40, and instructs the preparation of the raster data of the assigned pages, and instructs the execution of the development registration of the print resources relating to unassigned pages.