An image forming apparatus includes: an image carrier that carries a developed image that has been developed on a surface thereof using a developer; a transfer member that transfers the developed image from the image carrier to a belt-shaped member; an electric power supply unit that supplies electric power to the transfer member; a measurement unit that measures a combined resistance value of the image carrier, the belt-shaped member, and the transfer member; and a controller that controls the electric power supply unit. The controller controls the electric power supply unit such that the electric power supplied to the transfer member is changed from a predetermined first supply value to a second supply value, the second supply value being larger than the first supply value, when the combined resistance value measured by the measurement unit is lower than a predetermined combined resistance value.