In a print server, when page setting is made, a spot color name is extracted from a comment in an image drawing command and image data or a code of a job on a page (page layout) unit basis and a list for a spot color name of each page is generated. After that, a color separating process and an RIP are performed on the page unit basis, raster data of each of colors C, M, Y, and K and corresponding raster data of a spot color name is generated, after that, on the basis of CMYK values designated by the spot color name, the raster data of the spot color is composed with the raster data of each of the colors C, M, Y, and K, and the resultant is output. In such a manner, an overprint of an object designated in a spot color can be reproduced accurately.