Image forming apparatus

An image forming apparatus, comprising:

• an image carrying member that carries a toner image on a surface thereof;
• an intermediate transfer belt that is disposed adjacent to the image carrying member and that is rotatably supported, the intermediate transfer belt being endless;
• a primary transfer roller that makes contact with an inner circumferential surface of the intermediate transfer belt and that is disposed opposite the image carrying member across the intermediate transfer belt, the primary transfer roller primarily transferring the toner image carried on the image carrying member to the intermediate transfer belt by applying a primary transfer voltage to the intermediate transfer belt;
• a first belt support roller that is rotatably supported at a position downstream of the primary transfer roller with respect to a rotation direction of the intermediate transfer belt and around which the intermediate transfer belt is wound;
• a secondary transfer roller that is connected to a ground and that is disposed opposite the first belt support roller across the intermediate transfer belt, the secondary transfer roller secondarily transferring, with a predetermined secondary transfer current, the toner image to a sheet passing between the secondary transfer roller and the intermediate transfer belt;
• a second belt support roller that is rotatably supported downstream of the primary transfer roller, upstream of the first belt support roller, with respect to the rotation direction of the intermediate transfer belt, the second belt support roller making contact with the inner circumferential surface of the intermediate transfer belt;
• a current feeder that is connected to the first belt support roller, the current feeder passing in the secondary transfer roller the secondary transfer current as part of an output current that passes in the first belt support roller when an output voltage of a same polarity as the toner image is applied to the first belt support roller;
• a controller that controls the current feeder;
• a current sensor that has a lead member electrically connecting between the current feeder and the second belt support roller, the current sensor sensing a leak current passing from the first belt support roller via the intermediate transfer belt to the second belt support roller;
• a rectifier that is electrically connected between the second belt support roller and the ground, the rectifier shutting off a current passing from the second belt support roller to the ground if a voltage on the second belt support roller is less than a predetermined reference voltage, the rectifier permitting the leak current to pass from the second belt support roller to the ground if the voltage on the second belt support roller is equal to or more than the reference voltage,
• wherein
• the controller
• controls the output current such that the secondary transfer current has a current value resulting from subtracting the leak current from the output current and
• keeps the voltage on the second belt support roller less than the reference voltage when the lead member is in a conducting state.