PURPOSE: To enable accurately detecting the residual quantity of sheets in such a way that a modulating signal generator, in which different modulating signals are generated, is provided in the sheet holding tray, and their fitting positions can be read out using a sensor to be moved up and down.

CONSTITUTION: An intermediate plate 3 which is fixed with a wire 2 and moved up and down is provided in a sheet holding tray 1, and a sensor 7 is fixed in the intermediate plate 3. Besides, lamps L1WL3 are provided seriatim from the bottom in the vertical direction to a printed circuit board 6 which is installed in the tray, and different frequency signals are generated (lighted) in the lamps L1WL3. And, signals from the lamp L1WL3 are read out using the sensor 7, and the position of the intermediate plate which is integrated with the sensor 7, namely the residual quantity of the sheets is detected by the relation between the signals from the lamps L1WL3 and the threshold level of detecting of the sensor 7.