IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents trouble such as an abnormal image, ground stain and toner flying-off due to insufficient transfer and discharge by combining a toner with a carrier having charging power suitable for the charging property of the toner; therefore which allows stable image formation. SOLUTION: With respect to a black toner and a magenta toner different from each other in charging property, the black toner which is a low charging toner is combined with a carrier having a higher charging power and the magenta toner which is a high charging toner is combined with a carrier having a lower charging power. At this time, each of the black and magenta toners is combined with the corresponding carrier so that a charge buildup ratio Z calculated by Z[%]=(Q60/Q600)×100 is made 90-120[%], wherein Q600 is a charge quantity obtained when the carrier and the toner are mixed by stirring for 10 min under the condition of a toner concentration of 7[%]; and Q60 is a charge quantity obtained when they are mixed by stirring for 60 s under the same condition. COPYRIGHT: (C)2007,JPO&INPIT