An image forming system includes a portable terminal device, an image forming apparatus, and a marker registration circuit. The image forming apparatus prints a marker associated with location information of a user who has instructed execution of printing on a recording medium. The portable terminal device includes an information acquisition circuit and a position notification image output circuit. The information acquisition circuit photographs a marker printed on a recording medium using an imaging device so as to acquire the location information registered in the marker registration circuit, and the location information is associated with the marker photographed by the imaging device. The position notification image output circuit outputs a position notification image that notifies a position corresponding to the location information acquired by the information acquisition circuit to an output device.