Image forming apparatus and transfer device

A transfer device, comprising:

• a transfer section configured to transfer a toner image onto a medium;
• a power supply section configured to supply a transfer bias voltage of either a constant current or a constant voltage to the transfer section;
• and
• a control section configured to adjust a determination condition of determination for determining which system of a constant current system and a constant voltage system to use for supplying the transfer bias voltage on the basis of a detection result of a state of the toner image formed by the toner image forming section, and further configured to determine the system of the transfer bias voltage on the basis of an index value to be changed corresponding to electric resistance of the transfer section and the determination condition.

An image forming method, comprising:

• forming a toner image;
• transferring the toner image onto a medium;
• supplying a transfer bias voltage of either a constant current or a constant voltage to a transferring section;
• detecting a state of forming the toner image;
• applying a constant current or voltage to the transferring section to detect a resistance value of the transferring section;
• and
• determining which system of a constant current system and a constant voltage system to use for supplying the transfer bias voltage on the basis of a detection result of detecting the state of forming the toner image and a detection result of applying a constant current or voltage to the transferring section.