An image forming system includes: a folding unit that folds a sheet of paper to form a fold in the sheet; a creasing unit that, before the sheet is folded, produces a crease in the sheet at a fold position where the fold is to be formed; a crease-position adjusting unit that adjusts a crease position where the crease is to be produced; a fold-position adjusting unit that adjusts the fold position; a first input unit that receives an input specifying an amount, by which the crease position is to be adjusted; and a second input unit that receives an input specifying an amount, by which the fold position is to be adjusted, wherein when the fold position is adjusted by the second input unit, the crease position is also adjusted in synchronization with the adjustment of the fold position.