The present invention relates to a desk-top type color electro-photographic apparatus which is easy in use, small in size and light in weight, wherein maintenance such as changing its photosensitive member can be performed by a user and color adjustment is performed with high accuracy of less than 100 .mu.m. Developing units for four colors are placed in a rank, a single endless-belt-shaped photosensitive member being placed below them to form an approximately oval shape, the photosensitive member being touched with a transfer member on its major axis side to transfer each color of images. In addition to this, the photosensitive member is employed a cartridge type for easiness of user's maintenance and constructed such that highly accurate positioning between the body of apparatus and the cartridge can be performed. Effect of the eccentricity of pulleys is decreased by means of making the pulleys wrapped with the photosensitive member have the identical diameter and making the diameter of the transfer member integer times as large as that of the pulley.