| 摘要 |
[Problem] To make it possible to use a common optical sensor of high detection sensitivity as the optical sensor for detecting register marks for each color. [Solution] An optical sensor 91 is provided with a light source 911 for irradiating light on a register mark and a light-receiving element 912 for receiving light reflected by the register mark. The light source 911 comprises a white light source 911w, a blue LED 911b and a red LED 911r. When the register mark to be detected is yellow, only the blue LED 911b is turned on. When the register mark to be detected is blue, only the red LED 911r is turned on. When the register mark to be detected is red or black, only the white light source 911w is turned on. |
