An image forming apparatus includes a charging portion for charging an image
bearing
member, an exposure portion for exposing the image bearing member that has been
charged to form an electrostatic latent image, a developing portion for developing
the electrostatic latent image with developer, a transferring portion to which
a transferring bias under constant voltage control is applied to transfer a developer
image on the image bearing member onto other member, a test pattern forming portion
for forming a test pattern for image control on the image bearing member by supplying
developer by the developing portion to an area on the image bearing member in which
charging by the charging portion is effected and exposure by said exposure portion
is not effected, and a test pattern detection portion for detecting the test pattern
that has been transferred to the other member by the transferring portion, wherein
the value of the transferring bias upon transferring of the test pattern onto the
other member is set in accordance with the surface potential of the image bearing
member upon formation of the test pattern.
