A transfer roller is provided near a developing roller which is set, at a relative speed of substantially zero, in contact with a photosensitive drum to develop an electrostatic latent image on the photosensitive drum into a visual image. A toner transfer roller supplies a toner, that is, a one-component developing agent which is stored in a toner storage section to the developing roller and receives that toner which is unspent upon development from the developing roller. The unspent toner transferred to the toner transfer roller is brought into abutting contact with a mesh network of a toner separating member to separate the toner from the toner transfer roller over a predetermined effective length. By so doing it is possible to erase a developing hysteresis from the developing roller and, at the same time, collect the toner back into the toner storage section so that the collected toner is mixed with a fresh toner for use at the next developing cycle.