A seal member includes a seal surface that comes into contact with and slides with an end portion of an outer circumferential surface of a developing roller. The seal surface includes a first seal region configured of a plurality of first fiber bundles including a first fiber having a charge property that repels a developer, and a second seal region configured of a plurality of second fiber bundles including a second fiber having a charge property that attracts the developer, both extending in an inclined direction such that a portion thereof closer to an opening portion of a frame body of a developing unit is located further downstream in a rotating direction of the developing roller, and being alternately disposed in the rotating direction, and a proportion of a portion occupied by the second fiber bundles on the seal surface is at least 5% and not more than 60%.