Image forming apparatus generating electrostatic forces in first and second directions with a predetermined duty ratio

02D 2 D2D 02D 01L1 L0−4A duty ratio Du (%), denoted by (T/(TT))×100, is in the range of 60≦Du≦80; a magnetic carrier has a resistivity ρ which decreases in accordance with an increasing electric field strength, and a relative dielectric constant ∈ which increases in accordance with an increasing electric field strength; a product of a time constant ∈∈ρ(s) of electric charge decay in an electric field strength Edecided by a second peak voltage Vand a dark potential V, and an electric field strength Esatisfies a relation of 20≦∈∈ρ E(s·V/cm); and a time constant ∈∈ρ(s) and a relative dielectric constant ∈ in an electric field strength E, which is decided by a first peak voltage Vand a bright potential V, satisfy the following relations: ∈∈ρ(s)≦6.0×10, and 30≦∈.