A cleaning device of an image forming apparatus includes: a magnetic brush roller rubbing a surface of a photosensitive drum by a magnetic brush formed of a toner and carriers; a cleaning blade removing the toner remaining on a photosensitive drum; a toner concentration initialization control part, in order that toner-to-carrier ratio T/C of the magnetic brush formed on the magnetic brush roller falls within a predetermined range, controlling bias applied to the magnetic brush roller and an amount of the toner supplied from a developing device to the photosensitive drum.