PURPOSE: To detect exactly the remaining quantity of a toner in a hopper, and also to prevent the toner from sticking, by detecting an oscillating state of a magnetic oscillating member oscillated by a rotary magnetic force body.

CONSTITUTION: When a stirring plate 7 is driven to rotate in the direction as indicated with an arrow 6, a magnet 7a also rotates simultaneously. A magnetic oscillating member 9 moves upward when the magnet 7a approaches from the lower part, and stops the oscillation when it recedes. When a replenishing toner 1 of a sufficient quantity exists in a hopper 2, the member 9 is prevented from oscillation by a resistance force of the toner, and fixed at a fixed position. On the other hand, in case when the toner 1 in the hopper 2 decreases, the resistance force decreases gradually, the member 9 starts its oscillation within a range in which a magnetic force between the magnet 7a and the member 9 exceeds the resistance force, and in the end, the toner 1 is consumed almost completely, and when the resistance force is gone, the member 9 oscillates. A lever 10 is provided so as to show a decrease of the contained quantity of the toner 1 by operating intermittently a microswitch 11.