A letter producing system includes: a printing unit for performing printing on a paper sheet for enclosure and a paper sheet for envelope and outputting the paper sheet for enclosure before the paper sheet for envelope; an inserting and sealing unit for making an envelope from the paper sheet for envelope and inserting and sealing the paper sheet for enclosure in the envelope; an enclosure size obtaining section for obtaining size information of the enclosure; a paper output timing obtaining section for obtaining information of output timing of the first paper sheet for enclosure from the printing unit based on the size information of the enclosure; and a paper output control section for controlling timing of output of the first paper sheet for enclosure from the printing unit to the inserting and sealing unit based on the information of output timing.