An image forming apparatus includes an image forming unit to form an adhesive toner pattern in a predetermined bonding range of a sheet, outside a printable range in which an image according to image data is formed, a stacking unit to stack multiple sheets one on top of another, and a sheet binding device that includes a fusing device to fuse and fix the adhesive toner pattern formed on the multiple sheets to bind the multiple sheets together, and a bonding strength setting unit to determine, in accordance with a desired bonding strength, at least one of a number of color toners used for forming the adhesive toner pattern, a bonding manner, a number of pixels of the adhesive toner pattern, a toner area ratio of the adhesive toner pattern, and a layer thickness of the adhesive toner pattern.