An image forming apparatus and a control method thereof to improve quality of an image in consideration of a change in posture of a print media. The image forming apparatus can include a transferred unit on which a visible image is formed, a transferring unit to form a transfer region through which the visible image is transferred onto a print medium, along with the transferred unit, a bias supplying unit to supply bias to the transferring unit so that a transfer electric field is produced in the transfer region, and a controller to control the bias supplying unit to supply different first to third biases to the transferring unit while at least first to third regions of the print medium pass through the transfer region, respectively.