Patent ID: 8406650

Claim:
A developing device comprising: a developing tank for storing developer; a developing roller for bearing the developer so as to carry the developer to a photoreceptor provided outside the developing tank, the developing roller being provided to the developing tank so as to face the photoreceptor via an opening section of the developing tank; a carrying member for simultaneously stirring the developer in the developing tank and carrying the developer to the developing roller, the carrying member being provided to the developing tank so that the carrying member is provided on one side with respect to the developing roller while the photoreceptor is provided on the other side with respect to the developing roller; and an air path above the developing roller, the air path connecting the opening section of the developing tank to inside of the developing tank, the developing roller rotating so that an outer surface of the developing roller moves in a direction from the opening section to the inside while facing the air path and that the outer surface moves downwardly while facing the carrying member, the carrying member rotating so that its outer surface moves upwardly while facing the developing roller, the developing tank having a vent formed above the carrying member, and a filter provided to the vent, the filter being permeable to air but impermeable to the developer, wherein the filter has an area which is 1.74 times or more but 4.34 times or less larger than a ventilation area, which is an area of an inlet of the air path, the inlet being opened to the opening section, the rotation of the developing roller causing a first airflow directed from the opening section of the developing tank along the air path to the inside of the developing tank, the rotation of the carrying member causing a second airflow directed upwardly from between the developing roller and the carrying member, collision between the first airflow and the second airflow causing a third airflow directed from the inside of the developing tank through the filter to outside of the developing tank and further directed from the outside through the filter back to the inside of the developing tank.