An image forming apparatus includes: a first photosensitive drum for a monochrome printing mode; second and third photosensitive drums for a color printing mode; a moving unit moving a medium from the first photosensitive drum via the second photosensitive drum to the third photosensitive drum; charger devices for charging the photosensitive drums; transfer devices for transferring developer images on the photosensitive drums to the medium; and a control unit configured to control charging biases of the charger devices and transfer biases of the transfer devices. The control unit executes, in the monochrome printing mode, an energy saving control in which an absolute value of a charging bias applied to the charger device for the third photosensitive drum is smaller than an absolute value of a charging bias applied to the charger device corresponding to the second photosensitive drum.