Developing device and image forming apparatus

A developing device comprising:

• a first rotational body configured to carry a developer contained in a developer containing portion;
• a second rotational body disposed so as to face the first rotational body and configured to receive and carry toner included in the developer from the first rotational body, to convey the toner to a position at which the toner is transferred to a photosensitive member on which an electrostatic latent image is formed;
• a first generation portion configured to generate a potential difference between the first rotational body and the second rotational body;
• a second generation portion configured to generate a potential difference between the second rotational body and the electrostatic latent image;
• a first control portion configured to, when a rotation speed of the second rotational body is greater than or equal to a threshold previously determined, cause the first generation portion to generate a first potential difference that enables the toner in a predetermined amount defined in accordance with a reference density for a toner image to be formed on the electrostatic latent image, to be transferred from the first rotational body to the second rotational body, and cause the second generation portion to generate a second potential difference that enables the toner in the predetermined amount to be transferred from the second rotational body to the electrostatic latent image;
• and
• a second control portion configured to, when the rotation speed is less than the threshold previously determined, cause the first generation portion to generate a third potential difference that enables the toner in an amount exceeding the predetermined amount to be transferred from the first rotational body to the second rotational body, and cause the second generation portion to generate a fourth potential difference that enables the toner in the predetermined amount to be transferred from the second rotational body to the electrostatic latent image.