A developing device includes: a first developer carrier that is moved in a same direction as a moving direction of a latent image carrier at a faster linear speed than the latent image carrier; a second developer carrier that further develops the obtained toner image and that is moved in a same direction at a faster linear speed than the latent image carrier; and a bias output unit that outputs a developing bias to be applied to the second developer carrier. The developing bias includes a direct-current component and a non-rectangular alternating-current component whose waveform has a gentle edge at which a direction of an electric field between the second developer carrier and a background portion of the latent image carrier is changed to a direction in which the toner is moved from the background portion toward the second developer carrier.