When attachment of an unused photoconductor unit is detected, a mode is executed in which, during non-image formation, a first current flowing in a charging roller is detected when a photoconductor is re-charged without irradiation of light by a pre-exposure device after being charged and passing through a transfer position during non-image formation, and a second current flowing in the charging roller is detected when the photoconductor is re-charged with irradiation of light by the pre-exposure device after being charged and passing through the transfer position, and a current supplied to an LED lamp during image formation is controlled in accordance with detection results.