Developing device and image forming apparatus capable of shortening time required to circulate developer in circulation path

A developing device comprising:

• a housing in which a circulation path is formed by a first path through which a developer passed to a developing roll flows, a second path disposed offset from the first path in a direction of gravity, and a pair of connecting ports connecting the first path and the second path;
• and
• a transport member that operates in the housing to transport the developer in a determined direction, or a reverse direction to the determined direction, in the circulation path according to a torque applied for driving the transport member, wherein the transport member comprises a developer auger and is rotationally driven by a motor,
• wherein when the applied torque obtained during the transportation of the developer in the determined direction is determined to be equal to or less than a reference value, the transport member transports the developer in the determined direction,
• wherein when the applied torque obtained during the transportation of the developer in the determined direction is determined to be greater than the reference value, the transport member transports the developer in the reverse direction,
• wherein when the applied torque obtained after the transportation of the developer in the determined direction and during the transportation of the developer in the reverse direction is determined to be equal to or less than an allowable value, the transport member transports the developer in the determined direction.