PURPOSE: To detect a decrease in the remaining amount of toner securely and save the circumferential space of a toner container by detecting a magnet which varies in rotating locus with the amount of toner.

CONSTITUTION: A holding member 5 is projected radially from the rotating shaft 4 in the toner container, and an arm 5 which has a wide surface opposite in a rotational direction is supported on the member 5 freely shakably and energized by an energizing means 8 in the rotational direction of the shaft 4. The magnet 7 is fixed to the top part of the arm 6. Then a magnetic sensor 9 is provided near the locus that the magnet 7 draws when the shaft 4 rotates with the arm 6 raised by the means 8. Therefore when the amount of toner is sufficient, the opposite surface 6a receives resistance to fall the arm 6 as shown by an arrow B and the magnet 7 draws a track l2 of rotation, which is detected by the sensor 9, but when the remaining amount of toner becomes less, a track l2 of rotation is drawn and the sensor 8 detects the magnetic force of the magnet 7 securely to display that on a warning lamp, etc.