| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming apparatus for detecting a belt surface of an image carrier by means of an optical sensor, configured to reduce error of a detection value of the optical sensor even when a lot of irregularities are formed on the belt surface due to foreign substances or scratches, or when both increasing noise and decreasing noise, depending on the irregularities, are generated, and to reduce the amount of toner.SOLUTION: An image forming apparatus includes: spot diameter changing sections 59-61 which change a spot diameter of light emitted from an optical sensor 57 onto a belt surface of an image carrier 50; and a control section which calculates the number of detection values exceeding a predetermined value, out of detection values of the optical sensor 57 arranged in a predetermined rotation distance of the image carrier 50, as a noise count, to increase the spot diameter by the spot diameter changing sections 59-61, according to the calculated noise count. |
