To enable images whose image density and hue are adjusted to be formed on both sides by entirely reversely setting the forming orders of the color images formed by first and second color image units by using black toner and color toner.

The forming orders of the color images formed by the first and the second color image forming units 300a and 300b by using the black toner and the color toner are entirely reversely set. In the first color image forming unit 300a, is arranged on the downstream side of the color developing unit 13 of K arranged at the most downstream position of a photoreceptor drum 10 in the rotating direction out of the color developing units 13 of Y, M, C and K being the plural developing means arranged in the forming order of toner images. In the second color image forming unit 300b, is arranged on the downstream side of the color developing unit 13 of Y at the most downstream position of the drum 10 in the rotating direction out of the color developing units 13 of K, C, M and Y being the plural developing means arranged in the forming order of the toner images.