An image forming device, comprising: an endless belt stretched by a plurality of rollers; and a detection sensor located to face one of the plurality of rollers while sandwiching the endless belt between the detection sensor and the one of the plurality of rollers, the detection sensor reading information formed on the endless belt through use of reflection of light. A recessed part is formed, to catch foreign particles, on the one of the plurality of rollers at a position which is shifted in an axis direction of the one of the plurality of rollers with respect to a detection area on the endless belt to which light from the detection sensor is irradiated.