Developing unit, process cartridge, and image forming apparatus using toner to develop toner image

A developing unit comprising:

• a developing frame;
• a developer bearing member supported by the developing frame and including a magnetic-field generating member, the developer bearing member being configured to carry a developer having a magnetic property;
• a conveying member supported by the developing frame and including a rotation shaft and a sheet portion of which a first end is fixed to the rotation shaft and a second end is a free end, the conveying member conveying the developer to the developer bearing member;
• and
• a partition that partitions an inner space of the developing frame into a developing chamber in which the developer bearing member is disposed and a developer chamber in which the rotation shaft of the conveying member is disposed, the partition including an opening for communicating the developing chamber with the developer chamber,
• wherein, when the conveying member rotates, the free end of the sheet portion enters the developing chamber through the opening,
• wherein relations C >A and B >A are satisfied, where A is a distance from a rotation center of the rotation shaft to an upstream end of the opening in a rotational direction of the rotation shaft, B is a distance from the rotation center to a downstream end of the opening in the rotational direction, and C is a length from the rotation center to the free end of the sheet portion in an unbent state, and
• wherein the upstream end of the opening is lower in a direction of gravitational force than the downstream end of the opening at an orientation in use, and
• wherein the downstream end of the opening is lower in the direction of gravitational force than an upper end of the magnetic-field generating member at the orientation in use.