Patent ID: 7116933

Claim:
A developing unit constructed such that a thin layer of a developing agent is deposited on a developing roller by way of a magnetic brush formed on a magnetic roller, and the developing agent is transferred from the developing roller to a photosensitive drum for development, the developing unit comprising: first DC bias voltage generating means which generates a first DC bias voltage to be applied to the magnetic roller; second DC bias voltage generating means which generates a second DC bias voltage to be applied to the developing roller; first AC bias voltage generating means which generates a first AC bias voltage to be applied to the magnetic roller, the first AC bias voltage being superimposed on the first DC bias voltage; and second AC bias voltage generating means which generates a second AC bias voltage to be applied to the developing roller, the second AC bias voltage being superimposed on the second DC bias voltage, wherein the first AC bias voltage and the second AC bias voltage have frequencies identical to each other and phases reversed to each other.