A toner cartridge horizontally installed in an electrophotographic printer having a photoreceptor drum where an electrostatic latent image is formed by charging and exposure, and contributing to toner supply and development by being fixedly coupled to in the electrophotographic printer. The toner cartridge includes a housing filled with toner of a predetermined color, a development roller rotatably installed on the housing to face the photoreceptor drum and to supply the toner to the photoreceptor drum to develop an image by a difference in electrical potential, a supply roller rotatably installed in the housing in contact with the development roller and to control the toner to adhere to the development roller, and a guide member coupled to the housing to be disposed under the supply roller and to guide supply of the toner. When a diameter of the development roller is D2, the diameter D2 satisfies an inequality that 10.4≦D2≦22.1 mm.