A tandem-type image forming system comprises: a plurality of image forming apparatuses connected in series, the image forming apparatuses which respectively perform image formation on sides of a sheet, thereby performing a job, the image forming apparatuses including: a first image forming apparatus; and a second image forming apparatus provided upper than the first image forming apparatus in a sheet conveying direction, wherein the first image forming apparatus includes: a controlling section which controls transmission of image data generated based on printing data of the job received by the first image forming apparatus to the second image forming apparatus, and the second image forming apparatus includes: a controlling section which controls feeding of a sheet on which the image formation is performed based on the image data received from the first image forming apparatus.