An image forming system includes a conveyance processing portion, a setting processing portion, an insertion processing portion, and an operation control portion. The conveyance processing portion executes a conveyance process to convey a plurality of sheets placed on a sheet placing portion, sequentially to a sheet stack portion. When the insertion timing to insert the insertion sheet comes during an execution of the conveyance process, the insertion processing portion executes an insertion process to convey a sheet from the sheet supply source of the insertion sheet to the sheet stack portion. The operation control portion is configured to control operations of an image forming apparatus during execution of a sheet bundle output process based on the sheet type of the insertion sheet conveyed in the insertion process that is included in the sheet bundle output process, the sheet bundle output process including the conveyance process and the insertion process.