Image forming apparatus

An image forming apparatus comprising:

• an image carrying member in which a photosensitive layer is formed on an outer circumferential surface;
• a charging unit that charges the outer circumferential surface of the image carrying member to a predetermined surface potential;
• an exposure unit that exposes the outer circumferential surface of the image carrying member charged by the charging unit to form an electrostatic latent image with attenuated charging;
• a development unit that supplies a toner to the electrostatic latent image of the image carrying member to form a toner image;
• a transfer unit that transfers the toner image formed on the outer circumferential surface of the image carrying member to a member to which the toner image is to be transferred;
• a cleaning roller that removes and collects a substance adhered to the outer circumferential surface of the image carrying member;
• a voltage application unit that applies a predetermined voltage to each of the charging unit, the development unit, the transfer unit and the cleaning roller;
• a current detection unit that detects a current flowing between the image carrying member and the cleaning roller when the voltage application unit applies a collection voltage to the cleaning roller;
• and
• a control unit that controls the image carrying member, the charging unit, the development unit, the transfer unit, the cleaning roller and the voltage application unit,
• wherein the control unit
• applies, with the voltage application unit, the collection voltage to the cleaning roller when an image is formed,
• estimates a surface potential of the image carrying member based on the current detected by the current detection unit when the collection voltage is applied and
• changes the collection voltage and a rotation speed of the cleaning roller when the surface potential of the image carrying member is lowered.