Patent ID: 7826755

Claim:
An image forming apparatus capable of performing monochrome printing and color-printing in a switchable manner, comprising: a plurality of photoreceptor drums; a plurality of developing units; a single intermediate transfer element; a plurality of drives for driving the plural photoreceptor drums; a single development transformer for supplying voltage to the plural developing units; a cumulative operation time measuring unit for calculating cumulative operation time for which the photoreceptor drum for monochrome printing has been used in the monochrome printing; and, a controller for rotationally driving the photoreceptor drums for color printing by a predetermined angle, characterized in that the controller stops rotation of the photoreceptor drums for color printing during monochrome printing while applying the developing voltage from the single development transformer to all the developing units, and compares the cumulative operation time calculated by the cumulative operation time measuring unit with a cumulative operation threshold time and rotationally drives the photoreceptor drums for color printing by a predetermined angle when the cumulative operation time is determined to reach the cumulative operation threshold time, the controller changes a lapse of time before the photoreceptor drums for color printing are rotationally driven, in accordance with the total cumulative number of rotations of the photoreceptor drum for monochrome printing.