Patent ID: 7848671

Claim:
An image forming apparatus comprising: a first image forming portion, wherein the first image forming portion includes: a first image bearing member; first electrostatic latent image forming means for forming the first electrostatic latent image which is a predetermined polarity on the first image bearing member; first development means for developing the first electrostatic latent image on the first image bearing member to form a toner image charged to the predetermined polarity; and a first transfer member for electrostatically transferring the toner image to a transfer material; a second image forming portion disposed next to the first image forming portion, wherein the second image forming portion includes: a second image bearing member; second electrostatic latent image forming means for forming the second electrostatic latent image which is a polarity opposite the predetermined polarity on the second image bearing member; second development means for developing the second electrostatic latent image on the second image bearing member to form a toner image charged to the predetermined polarity; and a second transfer member for electrostatically transferring the toner image to the transfer material; transfer voltage applying means for applying transfer voltages to the first and second transfer members; first detection means for detecting (i) a current when the transfer voltage applying means applies a predetermined voltage to the first transfer member or (ii) a voltage when the transfer voltage applying means passes a predetermined current through the first transfer member; first determination means for determining the transfer voltage applied to the first transfer means for transferring the toner image on the first image bearing member to the transfer material based on the detection result of the detection means; and control means for controlling the transfer voltage applying means such that the voltage applied to the second transfer member is neither changed nor turned on and off in a period during which the first detection means detects the current passed through the first transfer member or the voltage applied to the first transfer member.