Image forming apparatus having a power supply common to primary transfer and secondary transfer

An image forming apparatus comprising:

• a plurality of image bearing members configured to bear a toner image;
• a rotatable endless intermediate transfer member provided with electrical conductivity, a plurality of primary transfer units being formed of the intermediate transfer member and the plurality of image bearing members, and a toner image being primarily transferred from the plurality of image bearing members in the plurality of primary transfer units;
• a secondary transfer member configured to contact an outer circumferential surface of the intermediate transfer member so that a secondary transfer unit is formed of the secondary transfer member and configured to secondarily transfer a toner image onto a transfer material from the intermediate transfer member in the secondary transfer unit;
• a transfer power supply configured to apply a transfer voltage to the secondary transfer member so that the secondary transfer member secondarily transfers the toner image from the intermediate transfer member onto a transfer material;
• a facing member configured to support an inner circumferential surface of the intermediate transfer member and to face the secondary transfer member across the intermediate transfer member;
• and
• a constant voltage element to be connected to the facing member,
• wherein the transfer power supply applies the transfer voltage to the secondary transfer member so that a potential required to primarily transfer the toner image in each of the primary transfer units is formed by the constant voltage element and the intermediate transfer member.