PURPOSE: A developing device of an electro-photo type printing machine is provided to stably contact a developing roller with a photosensitive drum due to a tangential friction force between the developing roller and the photosensitive drum. CONSTITUTION: A photosensitive drum(120) for forming an electrostatic latent image is rotatably mounted to a frame(110). A guide groove(115) is furnished to the frame and guides a developing roller(150) toward the photosensitive drum. At the initial position, the developing roller is separated from the photosensitive drum, a central shaft(M) connecting centers of the developing roller and the photosensitive drum has a predetermined inclined angle(theta2) between a progressive shaft(L) of the developing roller transferred from the guide groove. The inclined angle(theta2) is preferably within 0-30 degrees.
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