IMAGE FORMATION DEVICE

An image forming apparatus comprising: a charging device that charges an image bearing member; an exposure device that forms said electrostatic image by exposing a surface of said image bearing member; a developing device that has a developer carrying member on which a developer including a toner and a magnetic carrier is carried; and a power supply that applies a developing bias on said developer carrying member; wherein said developing bias is an oscillating voltage having a peak voltage V 1 a peak voltage V 2 ; a duty ratio Du (%); said magnetic carrier has a characteristic that: said magnetic carrier has a resistivity Á which decreases in accordance with an increasing electric field strength, and a relative dielectric constant µ which increases in accordance with an increasing electric field strength; a product of a time constant µ 0 µÁ(s) of electric charge decay, which is denoted by a dielectric constant of a vacuum µ 0 , the relative dielectric constant µ of said magnetic carrier, and said resistivity Á in an electric field strength E 2D decided by said peak voltage V 2 and said dark potential V D , and said electric field strength E 2D satisfies a relation of 20 ‰¤ µ 0 µÁ E 2D (s·V/cm); and said time constant µ 0 µÁ(s) and said relative dielectric constant µ in an electric field strength E 1L , which is decided by said first peak voltage V 1 and said bright potential V L , satisfy the following relations: µ 0 µÁ(s) ‰¤ 6.0 x 10 -4 , and 30 ‰¤ µ.