PURPOSE: To obtain a color image having no color mixture even if the potential on a toner image of the 1st color which is already formed varies by varying and controlling the bias voltage value of the next development of the 2nd color according to the potential on the toner image of the 1st toner after electrostatic recharging.

CONSTITUTION: A two-color recording device charges a photosensitive drum 1 electrostatically and uniformly by an initial charger 2, and the 1st exposure system 3 forms the 1st latent image, which is developed in the 1st color by the 1st developing device 4. Then, a recharger 5 charges the photosensitive drum again, the 2nd latent image is formed by the 2nd exposure system 6 and developed in the 2nd color by the 2nd developing device 7, and the toner images of the two colors are transferred and fixed at a time to obtain two-color record. Then, the potential on the toner image of the 1st color after the recharging is measured by a surface potential meter 21 and a control part 20 controls the developing bias variable power source 17 of the 2nd developing device 7 according to the potential so that the developing bias voltage of the 2nd color is invariably lower than the potential on the toner image of the 1st color.