An insertion system includes a folding device to perform either single-sheet folding to fold a single sheet at a time or batch folding to fold multiple sheets together at a time, an insertion device to insert into an envelope the sheet folded by the folding device, and a batch setting unit to designate either the single-sheet folding or the batch folding from a folding and insertion menu for multiple sheets at a time when the multiple sheets are processed by the folding device and the insertion device.