An image forming apparatus includes first photosensitive members, first chargers for charging the first photosensitive members, developer carriers for supplying developer to the first photosensitive members, a first charging-bias applying unit that applies charging biases to the first chargers, development-bias applying units for applying development biases to the corresponding developer carriers, a charging-current sensing unit that separately senses a charging current flowing in each of the first chargers, and a control unit that controls the development biases based on the sensed charging current. When a difference between a reference charging-current value and a detected charging-current value exceeds a predetermined value, if the detected charging-current value is larger than the reference charging-current value, the control unit increases an absolute value of a development bias applied to a developer carrier corresponding to the charger having the difference exceeding the predetermined value.