Developing device having inductance sensor

A developing device comprising:

• a developer bearing member which bears developer including toner and carrier to develop an electrostatic latent image formed on an image bearing member;
• a developing container which accommodates the developer;
• a conveying screw which conveys the developer accommodated in the developing container;
• and
• an inductance sensor which includes a detecting portion which detects magnetic permeability of the developer accommodated in the developing container,
• wherein in a state that a predetermined magnetic material is disposed at a position in contact with the detection portion, an output value when the detection unit detects magnetic permeability of the predetermined magnetic material is A, and
• in a state that the predetermined magnetic material is disposed 1 mm away from the detection portion in a vertical direction, an output value when the detection unit detects magnetic permeability of the predetermined magnetic material is B, with B/A≥0.1 being satisfied,
• wherein the conveying screw includes:
• a rotary shaft;
• a blade which is spirally formed on an outer circumference of the rotary shaft;
• and
• a rib formed as to protrude outwardly from the outer circumference of the rotary shaft,
• wherein the rib is disposed opposite the detection portion with respect to a conveying direction of the conveying screw, and
• wherein the rib is provided with a magnet, with magnetic flux density of the magnet being in the range of 20 mT to 60 mT.