Developing device including spiral blade for conveying developer while rotating and image forming apparatus

A developing device comprising:

• a housing which houses a developer,
• a replenishment port through which the developer is replenished to the housing;
• a spiral blade which stirs the developer in the housing while conveying the developer in a predetermined conveyance direction;
• a discharge port through which the developer conveyed by the spiral blade is discharged;
• a circular regulating member which is disposed between a downstream end portion of the spiral blade in the conveyance direction and the discharge port, and regulates a conveyance of the developer to the discharge port;
• and
• a rotational shaft portion provided with the circular regulating member and the spiral blade, in which a center of the rotational shaft portion coincides with a center of the circular regulating member;
• and
• a reverse spiral blade provided between the circular regulating member and the discharge port on the rotational shaft portion, spirally formed in a winding direction opposite to that of the spiral blade, and conveying the developer in a direction opposite to the conveyance direction, wherein
• the circular regulating member has a lack portion penetrating in the conveyance direction,
• the lack portion is a slit formed along a radial direction of the rotational shaft portion and is separated from the downstream end portion of the spiral blade in a circumferential direction of the rotational shaft portion,
• a part of the developer conveyed along the conveyance direction and passing over the circular regulating member is discharged from the discharge port, while the developer passing through the lack portion is pushed back by the reverse spiral blade and is not conveyed to the discharge port,
• the smaller an amount of the developer passing through the lack portion, the larger a discharge amount of the excessive developer discharged through the discharge port, and
• the longer a distance between the lack portion and the downstream end portion of the spiral blade along the circumferential direction of the rotational shaft portion, the smaller an amount of the developer passing through the lack portion.