| 摘要 |
PURPOSE:To reduce the number of parts and the cost of a device by eliminating a toner quantity sensor detecting the toner quantity in a hopper. CONSTITUTION:A toner concentration sensor 17 detects the reflection density of a patched picture obtained from a standard index plate 18 to control the concentration of the toner in a developing tank 10c. The device is provided with a counter means counting detecting signals from a paper eject sensor 19 and a display 21 prompting the hopper 10a to replenish toner. When the detecting signal from the toner concentration sensor 17 does not reach a set value and a previously set number of copies is counted, a toner concentration control part 20 outputs a toner requiring signal. Consequently, toner replenishment is prompted without using the toner quantity sensor detecting the quantity of the toner in the hopper 10a. Thus, the number of parts and manufacturing costs can be reduced. |
