An image formation apparatus such as a color copier or color printer comprises a plurality of development units, a development bias power source to supply power sources to the development units, a switch for allowing the output power of the development bias power source to be supplied to the development unit selected in accordance with a sequence control signal for image formation generated from a sequence controller, and a power supply control circuit to selectively to supply the output power of the development bias power source to the development unit which is developing only for a development period of time of each development unit. The development units are fixedly arranged near the photosensitive drum on which an electrostatic latent image is formed. The development bias power source includes both an AC component and a DC component. Since the amplitude, frequency, DC potential, and the like of the development bias power source are switched for each development unit selected, it is sufficient to use only one expensive power source. In this manner, image deterioration by the mechanical vibration due to the movement of the development unit can be eliminated.