An image forming machine comprising a single layer dispersion type photoconductor drum, a charging device for charging the surface of the photoconductor drum to a specific polarity, and a developing roller for conveying a developer to the surface of the photoconductor drum having a latent electrostatic image formed thereon; wherein the photoconductor drum and the developing roller are adapted to contact each other at their surfaces and to be rotationally driven in reverse directions; and the photoconductor drum has a diameter set at 10 to 20 mm, while the developing roller has a diameter set at 90 to 110% of the diameter of the photoconductor drum.