Developing device and image-forming apparatus

A developing device comprising:

• a developer-carrying member that is substantially tubular, that accommodates a magnetic source that generates a magnetic force for carrying a developer containing magnetic particles on an outer surface thereof, and that rotates in a circumferential direction thereof;
• a developer control member that is disposed opposite the developer-carrying member and that controls the thickness of a layer of the developer carried on the outer surface of the developer-carrying member;
• a supply member that is disposed opposite the developer-carrying member upstream of the developer control member in a rotational direction of the developer-carrying member and that rotates to transport the developer in a rotation axis direction thereof and to supply the developer to the developer-carrying member;
• and
• a rotating member that is rotatably disposed opposite the developer-carrying member at a position where the rotating member is submerged in the developer between the developer control member and the supply member and that rotates to supply the developer from between the developer control member and the supply member to the supply member,
• wherein:
• the supply member includes a rotating shaft and a vane portion disposed therearound;
• the developer control member is disposed below the developer-carrying member in a vertical direction;
• and
• about ¼≦A/B≦about ½ is satisfied, where A is a shortest distance between a tangent to the outer surface of the developer-carrying member at a layer control position opposite the developer control member and an outer surface of the rotating member, and B is a shortest distance between the tangent to the outer surface of the developer-carrying member at the layer control position opposite the developer control member and an outer surface of the rotating shaft of the supply member.