Developing device

1. A developing device, comprising:

a developing container configured to store a developer including a non-magnetic toner and a magnetic carrier;

a cylindrical developing sleeve having a plurality of grooves which are respectively formed in a direction which intersects a circumferential direction of the developing sleeve on an outer surface thereof and configured to rotate while carrying the developer on the outer surface;

a developer regulating member configured to regulate an amount of the developer carried by the developing sleeve; and

a magnetic field generating portion disposed on an inner side of the developing sleeve and including a plurality of fixed magnetic poles which have at least a drawing-up pole which draws up the developer in the developing container and bears the developer on the outer surface of the developing sleeve, and a cut pole which is disposed to be adjacent to the drawing-up pole on a downstream side of the drawing-up pole in a direction of rotation of the developing sleeve and to be in the vicinity of the developer regulating member,

wherein the plurality of fixed magnetic poles are configured to form a Fr attenuation area in which Fr attenuates toward the cut pole side from the drawing-up pole side between a peak of a magnetic flux density of the drawing-up pole and a peak of a magnetic flux density of the cut pole, and a Fθ reverse area in which Fθ is oriented towards an opposite direction to the direction of rotation of the developing sleeve between the peak of the magnetic flux density of the drawing-up pole and the peak of the magnetic flux density of the cut pole where Fr is a magnetic force in a direction toward the center of the developing sleeve and Fθ is a magnetic force in a tangential direction of the outer surface of the developing sleeve,

wherein a pitch interval of the plurality of grooves of the developing sleeve is shorter than a length of the Fθ reverse area in the direction of rotation of the developing sleeve.

2. The developing device according to claim 1 , wherein, when an angle which is made of a line that links the peak of the magnetic flux density of the drawing-up pole and the center of the developing sleeve and a line that links the peak of the magnetic flux density of the cut pole and the center of the developing sleeve is A, and an angle which is made of lines that link both ends of the Fr attenuation area and the center of the developing sleeve is B, 0.12≦B/A<0.65 is satisfied.

3. The developing device according to claim 2 , wherein, when an angle which is made of the lines that link both ends of the Fθ reverse area and the center of the developing sleeve is C, 0.12≦C/A<0.40 is satisfied.

4. The developing device according to claim 3 , wherein, when an angle which is made of lines that link the centers of the adjacent grooves among the plurality of grooves and the center of the developing sleeve is D, 2.5≦C/D<5.0 is satisfied.

5. The developing device according to claim 1 , wherein, when an angle which is made of the line that links the peak of the magnetic flux density of the drawing-up pole and the center of the developing sleeve and the line that links the peak of the magnetic flux density of the cut pole and the center of the developing sleeve is A, and an angle which is made of lines that link both ends of the Fθ reverse area and the center of the developing sleeve is C, 0.12≦C/A<0.40 is satisfied.

6. The developing device according to claim 1 , wherein, when an angle which is made of the lines that link both ends of the Fθ reverse area and the center of the developing sleeve is C, and an angle which is made of lines that link the centers of adjacent grooves among the plurality of grooves and the center of the developing sleeve is D, 2.5≦C/D<5.0 is satisfied.

7. The developing device according to claim 1 , wherein a depth of each of the plurality of grooves is formed to be equal to or greater than a diameter of a particle of the magnetic carrier and a width of each of the plurality of grooves is formed to be equal to or greater than the diameter of the particle of the magnetic carrier.

8. The developing device according to claim 1 , wherein an absolute value of Fr between the peak of the magnetic flux density of the drawing-up pole and the peak of the magnetic flux density of the cut pole is set within a range of 1×10 −8 (N) to 1.5×10 −7 (N).