An image forming apparatus is described. The image forming apparatus may include an image carrier on which an electrostatic latent image is formed; a developing agent carrier that transforms the electrostatic latent image into a visible image by supplying a developing agent to the image carrier; and a developing agent cartridge that accommodates a developing agent to be supplied to the developing agent carrier, arranged so as to be opposed to the developing agent carrier in a longitudinal direction of the developing agent carrier, and formed with an opening for horizontally passing the developing agent in a position horizontally opposed to the developing agent carrier.