An image output system comprising a document server, an information processing terminal, and an image output device connected through a network, wherein the information processing terminal is adapted to designate an output target document out of documents stored in the document server and instructs output of a job to the image output device, if the image output device is not a direct output compatible device capable of outputting a file format of the output target document as it is, the document server is adapted to convert the output target document to image data in a given file format, generate job data, and transmit the job data to the image output device, the job data containing job control information defining output setting and job substantive information designating the image data as an output target in a page description language, and the image output device is adapted to output the output target document based on the job data output from the document server, wherein the document server includes: a prototype data generating unit that is adapted to generate job control information and job prototype data containing the job control information, the job control information defining output setting to be applied during output of the output target document; an image converting unit that is adapted to read the output target document and convert the output target document to image data in the given file format, the image data comprising a plurality of pixels, if the image output device is not a direct output compatible device capable of outputting a file format of the output target document as it is; a job generating unit that is adapted to generate job data by adding job substantive information to the job prototype data generated by the prototype data generating unit, the job substantive information designating the image data generated by the image converting unit as an output target in a page description language; and a job outputting unit that is adapted to output the job data generated by the job generating unit to the image output device, wherein the prototype data generating unit is adapted to generate dummy image data in the given file format, the dummy image data having the same file format as the image data, based on attribute information about the output target document and generate the job prototype data further containing job substantive information, the dummy image data having the same attribute as the attribute information, the dummy image data having the same page size and the same number of pages as the output target document, and the dummy image data being constructed by the same pixels arranged continuously, the job substantive information designating the dummy image data as an output target in a page description language, and the prototype data generating unit is further adapted to supply the dummy image data and attribute information to a printer driver compatible with the image output device as an output destination (p 12, 2-4), and in response the device driver is adapted to generate the job substantive information designating each page of the dummy image data as an output target in the page description language and is further adapted to add the job control information to a header of the job substantive information thereby generating the job prototype data, the job generating unit is adapted to generate job data by replacing the dummy image data in the job substantive information of the job prototype data by the image data generated by the image converting unit, in response to receiving the job data from the job generating unit, a job output unit is adapted to output the acquired job to the image output device as an output destination and is further adapted to make the output device execute the job. a prototype data generating unit that is adapted to generate job control information and job prototype data containing the job control information, the job control information defining output setting to be applied during output of the output target document; an image converting unit that is adapted to read the output target document and convert the output target document to image data in the given file format, the image data comprising a plurality of pixels, if the image output device is not a direct output compatible device capable of outputting a file format of the output target document as it is; a job generating unit that is adapted to generate job data by adding job substantive information to the job prototype data generated by the prototype data generating unit, the job substantive information designating the image data generated by the image converting unit as an output target in a page description language; and a job outputting unit that is adapted to output the job data generated by the job generating unit to the image output device,