To prevent the lowering of image forming capability at the time of successive forming images in which monochromatic images and color images coexist.

In the image forming device to print a color or monochromatic image on recording paper fed by the image forming means of respective colors such as YMCK, in the case that several recording media are successively fed, and the monochromatic image is formed on a preceding recording medium and the color image is formed on a following recording medium, a timing signal A corresponding to the following recording medium is outputted before a timing signal B meaning image forming start corresponding to the preceding recording medium.