In an image forming apparatus wherein plural developing devices 3 have alternating electric field applying mechanisms 4, the alternating electric field applying mechanisms 4 have alternating electric field changing mechanisms 7 for reducing the degree of the action of the alternating electric field on at least one of the developing devices 3 which are later in development order, to a level which is lower than that in the preceding step. As required, at least one of the transferring devices 5 which are later in transfer order has a transfer force changing mechanism 8 for increasing the force of transfer to a transfer medium 6 applied to a color-component toner image on an image carrier 1, to a level which is higher than that in the preceding step. Furthermore, an operation condition judging mechanism 9 may judge whether preset transfer failure conditions are satisfied or not, or environmental conditions may be considered by an environmental condition adjusting device 10.