An image forming apparatus includes an image carrier, a developing device, a voltage applier, a current detector, a cleaning blade, and a control device. The control device acts as a measurer and an estimator. The measurer changes the DC bias to a first value and a second value, and acquires a first magnitude of the developing current corresponding to the first value, and a second magnitude of the developing current corresponding to the second value, from the current detector. The estimator calculates a current ratio between the first magnitude and the second magnitude, and estimates deterioration status of the cleaning blade, according to the value of the current ratio.