An image forming apparatus having an image forming unit to form an image on a sheet, includes a sheet inserting unit configured to insert one or more of a first insertion sheet and a second insertion sheet at one or more predetermined insertion positions in a plurality of sheets, in a case where the plurality of sheets are output by the image forming unit. The image forming apparatus also includes a control unit configured to control the sheet inserting unit to prevent the sheet inserting unit from inserting both the first insertion sheet and the second insertion sheet at the same predetermined insertion position in the plurality of sheets.