By a conventional mechanism for detecting a position of a knob of a toner bottle, the detection of the presence or absence of the toner bottle could not be effected. So, by providing an optical sensor on the inner surface of an interchange door opposed to the knob of the toner bottle, it is possible to effect the detection of the presence or absence of the toner bottle, and the detection of the position of the knob, i.e., the opening and closing of a shutter of the toner bottle.