Filter holding device, developing device, process cartridge, and image forming apparatus

A filter holding device comprising:

• an opening portion to communicate between an inside and an outside of the filter holding device;
• and
• a filter disposed in the opening portion, the filter including:
• a first side located adjacent to the inside of the filter holding device;
• and
• a second side located adjacent to the outside of the filter holding device,
• the filter having a larger weight density per unit volume at the second side than a weight density per unit volume at the first side,
• the filter having a larger cross-sectional area perpendicular to a communication direction at the second side than at the first side,
• the filter comprises a flange at the second side, the flange, being a part of the filter, having a first cross-sectional area perpendicular to the communication direction larger than a second cross-sectional area perpendicular to the communication direction of other portions of the filter and having the larger weight density per unit volume than the weight density per unit volume at the first side, and
• the opening portion has a rim as a wall portion, the rim having a step portion having a first opening area perpendicular to the communication direction larger than a second opening area perpendicular to the communication direction of other portions of the opening portion,
• wherein the flange is in contact with the step portion, the first cross-sectional area of the flange is larger than the first opening area of the opening portion, and the second cross-sectional area of the other portions of the filter is larger than the second opening area of the other portions of the opening portion.