Image forming device with transfer unit

An image forming device for transferring a toner image formed on an image carrier onto a transfer medium which is in close contact with the image carrier comprising:

• a guide member for guiding the transfer medium toward a transfer position of the image carrier,
• a transfer unit for charging the transfer medium guided to the transfer position,
• a power source which supplies power to the transfer unit,
• a feedback circuit for controlling the output of the power source so as to maintain at a constant value the amount of electric current obtained by excluding the amount of electric current that flowing to the guide member from the electric current that flowing from the transfer unit to the transfer medium will be constant, and;
• said feedback circuit having a circuit which splits the electric current flowing from the guide member and routes it toward a grounded high resistance element and a constant voltage element connected to the feedback side of the power source.