| 摘要 |
PROBLEM TO BE SOLVED: To reduce the power consumption by obtaining such circuit constitution that the supply/disconnection of a power source to supply power to plural detection means detecting the existence of toner, with which a developing device is filled, can be selected by a controller. SOLUTION: Each developing unit is filled with toner of each color, and the toner is supplied to a photoreceptor from a developing roll 5a at the time of developing. Light emitted from a light emitting sensor 501 is transmitted through an optical path 504 or intercepted in accordance with the existence of the toner in the developing unit. When a light receiving sensor 502 attached to a position where the transmitted light is received receives the light, an inside transistor 502a is turned on, and when it does not receive the light, the transistor 502a is kept in an off-state. Then, the existence of the toner is detected according to the difference of the state. The sensors 501 and 502 are controlled by a sensor turning on/off circuit 500 and optionally turned on/off according to an instruction from a CPU. In the case toner existence detecting function is not required, the power source of the detection means is turned off according to a control signal from the controller so as to reduce the power consumption. |
