When continuous printing in which color print and monochromatic print are mixedly present is to be effected, the distance between recording sheets is greatly widened to avoid problems when changeover takes place from monochromatic print to color print and therefore, the printing capability (the number of prints per unit time) is reduced.When in an image processing apparatus for forming a color or monochromatic image on a recording sheet conveyed, by yellow, magenta, cyan and black image forming means, a plurality of recording mediums are continuously conveyed and a monochromatic image is to be formed on a preceding recording medium and a color image is to be formed on a succeeding recording medium, a timing signal A corresponding to the succeeding recording medium is outputted earlier than a timing signal B indicative of the start of image formation corresponding to the preceding recording medium.