US Patent 7512358 Developer supply device and developer

A toner leakage restrainer is disposed in an opening formed in a development cartridge case. In the development cartridge, the toner which contains fine particles only in a small amount is accommodated such that fusion bonding of the toner to the lower film is not caused even when ten thousand sheets are printed in succession. In the toner, a ratio of the powder particles having a circle equivalent diameter of 3 to 20 μm and a circularity of 0.98 or more to the entire powder particles is 60% or more based on the number of the particles, and a ratio of the powder particles having a circle equivalent diameter of 3 μm or less to the entire particles is 35% or less based on the number of particles.