Image forming apparatus

An image forming apparatus comprising:

• an image forming portion including:
• an image carrying member having a photosensitive layer formed on a surface thereof;
• and
• a developing device having a developer carrying member that is disposed opposite the image carrying member and that carries two-component developer containing magnetic carrier and toner, the developing device attaching the toner to an electrostatic latent image formed on the image carrying member to form a toner image;
• a development voltage power supply that applies a development voltage at least containing a direct-current voltage to the developer carrying member;
• a current detection mechanism that detects, when the development voltage is applied to the developer carrying member, a development current passing between the developer carrying member and the image carrying member;
• and
• a control portion that controls the image forming portion and the development voltage power supply,
• wherein
• the development current includes an image part current passing between the developer carrying member and an image part of the image carrying member and a blank part current passing between the developer carrying member and a non-image part of the image carrying member, and
• the control portion estimates an amount of charge on the toner based on the blank part current detected by the current detection mechanism.