PURPOSE: To prevent toner staining at the time of replenishing a developer, by providing a developer vessel and a hopper with its mobile cap and its functioning member, respectively, and when the vessel is fitted to the hopper, causing each member to move the mobile cap of the other side to form each opening.

CONSTITUTION: The outer and inner caps 23, 24 of the ejection part 21 of the developer vessel 2 are provided with larger openings 231, 241, and with smaller openings 232, 242, the opening of each couple being opposite to each other and same as each other in size. The main body 31 of the opening part of the hopper 1 and the mobile cap 32 are provided with the like openings. When the vessel 2 is fitted to the hopper 1 and the vessel 2 is turned, the protruded member 315 of the main body 31 inserted into the blind hole of the inner cap 24 turns it, and the protruded member 235 of the outer cap 23 inserted into the groove 325 of the mobile cap 32 turns it, thus forming the openings. The larger opening serves as a feed inlet of the developer, and the smaller one serves as the reverse outlet of the air. Hence, the developer can be smoothly replenished without scattering.