| 摘要 |
PROBLEM TO BE SOLVED: To steadily and accurately detect an amount of toner. SOLUTION: The maximum bottom value (value of the largest amount of light) of a light receiving signal for light made incident on a light receiving element 22 is held in a bottom hold part 30, and when the held value (value of the largest amount of light) is held as 100%, a threshold is set to arbitrary x% (x<100) by an automatic threshold-setting part 31, thereby relationship between the light receiving signal and the threshold is kept constant. Thus, even in case the amount of received light decreases due to toner sticking to a light detection channel, the amount of toner can be detected steadily and accurately. |
