Patent ID: 7088933

Claim:
An image forming apparatus having: charging means for charging an image bearing member; latent image forming means for exposing said charged image bearing member to light, thereby forming an electrostatic latent image having an area of image portion potential and an area of non-image portion potential thereon; developing means for applying a developing bias to a developer carrying member carrying a developer, thereby developing said electrostatic latent image on an opposite portion of said image bearing member, which is opposed to said developer carrying member, and forming a developer image on an area of said image portion potential; transferring means for electrostatically transferring the developer image on said image bearing member to a transfer medium in a transferring portion, said transferring means having a transfer member capable of nipping said transfer medium between it and said image bearing member, and charge supplying means capable of supplying charges to said transfer member; and control means for detecting a voltage-current characteristic regarding said transfer member by applying a test bias to said transferring means which contacts said image bearing member during a non-transferring operation, and determining a transfer supplying condition to said transfer member during a transferring operation on the basis of a result of said detection, wherein said control means determines said transfer charge supplying condition on the basis of a first detection result obtained by performing said detection of applying said test bias to said transferring member which contacts an area of said non-image portion in said electrostatic latent image on said image bearing member which passes said opposite portion when said developing bias is not applied, and a second detection result obtained by performing said detection of applying said test bias to said transferring member which contacts an area of said non-image portion in said electrostatic latent image on said image bearing member which passes said opposite portion when said developing bias is applied.