| 摘要 |
PROBLEM TO BE SOLVED: To provide a developing device capable of preventing developer from retaining on the detecting surface of a toner concentration sensor and toner from fusion-sticking thereto, thereby accurately measuring the toner concentration of the developer. SOLUTION: Two slits 10 are formed on the peripheral wall of a developer casing 1 in which the developer is stored by leaving space in between. A part of an endless belt 12 laid on a pair of belt pulleys 11 arranged on the outside of the casing 1 is guided into the casing 1 through the slits 10. The one surface of the part of the belt 12 existing in the casing 1 becomes a contact surface 13 coming into contact with the developer. The toner concentration sensor 5 detects the toner concentration of the developer in the casing 1 through the peripheral wall of the casing 1 and the part of the belt 12 existing in the casing 1.
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