An image forming apparatus includes an image bearing member, a charging roller and a pair of gap forming members. The image bearing member has a photoconductive surface including an image forming area for bearing an electrostatic latent image. The charging roller has a circular cross section with a first radius and a metallic core having a rotational axis of the charging roller, in parallel with and close to the image bearing member, and a charging surface for charging the photoconductive surface. The pair of gap forming members form a gap at least between the image forming area and the charging surface. Each of the pair of gap forming members have a circular cross section with a second radius such that a ratio of the second radius to the first radius is substantially constant through a whole rotational phase of the charging roller.