An image forming apparatus has a photoconductive member, and a developing roller develops a latent image on the photoconductive member by a first alternating-current bias in the form of a rectangular wave. The following relationships are satisfied in calculating the duty ratio (D1) of the first alternating-current bias using an application period of voltage in a direction to transfer the toner from the developing roller towards the photoconductive member as a positive period: a CV value in the number particle size distribution of the toner is ≦25%, 4 μm≦Dt≦7 μm, 105 Ω·cm≦pv≦109 Ω·cm, 0.4 μm≦Ra≦1.5 μm, and 35%≦D1≦75%. where Dt denotes the volume average particle diameter of the toner, pv denotes the intrinsic resistance value of a developing roller surface, Ra denotes the arithmetic average roughness of the developing roller surface.