An image forming system includes: an image forming unit that forms a toner image on a sheet; a post-processing unit that performs post-processing to the sheet; a conveying unit that conveys the sheet from the image forming unit to the post-processing unit; a discharge member that is arranged between the image forming unit and the post-processing unit in a sheet conveying direction, and discharges static electricity from the sheet conveyed by the conveying unit; a voltage applying unit that applies to the discharge member a discharge voltage for discharging static electricity from the sheet; and a control unit that accelerates a conveying speed of the sheet when the discharge voltage is applied by the voltage applying unit, and controls the conveying unit to vary acceleration timing for accelerating the conveying speed of the sheet in accordance with a type of the post-processing.