An image forming apparatus and a transfer device thereof are disclosed. The transfer device includes an intermediate transfer belt, at least one intermediate transfer belt roller to maintain tension in the intermediate transfer belt, transfer rollers to press the intermediate transfer belt to image carriers and a state changing device to change an operating state between at least a first state, in which the tension in the intermediate transfer belt is released, and a second state, in which select ones of the transfer rollers are separated from the intermediate transfer belt.