Patent ID: 8548343

Claim:
An image forming apparatus comprising: an image carrying member that carries a toner image; a detecting section that detects passage of a mark, on the image carrying member, at a plurality of predetermined detection positions; and a linear-speed deriving section that determines a linear speed of the image carrying member from the times at which the detecting section detects the passage of the mark, wherein the detecting section causes measurement light to be incident upon the detection positions, detects reflected portions of the measurement light from the detection positions, and outputs an output signal corresponding to the detected portions of light, the linear-speed deriving section specifies the times at which the plurality of detecting sections detects the passage of the mark, based on the output signals, the detecting section includes light-emitting elements that emit the measurement light and photodetectors that receive the reflected portions of the measurement light, the light-emitting elements and the respective photodetectors forming pairs located at positions corresponding to the detection positions, and a light-emitting element corresponding to one of the detection positions emits the measurement light and the mark is detected at the one of the detection positions and a light-emitting element corresponding to a remaining detection position does not emit the measurement light.