According to an embodiment, a transfer device includes: an image carrier (80) from which an image is transferred onto a transfer medium using electrostatic toner, the image carrier (80) being applied with a direct current voltage superimposed with an alternating current (AC) voltage as a transfer bias. An output voltage of a power source (110) for applying the voltage is controlled so that a current level of a direct current component output from the power source (110) is kept at a specified current level.
