Image forming method and apparatus for effectively performing a cleaning operation of a transfer member

An image forming apparatus includes an image bearing member configured to bear an image on a surface thereof, a transfer unit configured to transfer the image formed on the surface of the image bearing member onto a recording medium, a bias applying unit configured to apply a bias voltage to the transfer unit to remove a developer adhered on a surface of the transfer unit to the surface of the image bearing member, a detecting unit configured to detect a width of the recording medium in a sheet conveyance direction, and a control unit configured to determine whether a cleaning operation of the transfer unit is performed, based on the width of the recording medium detected by the detecting unit and a number of the recording medium printed.