A developing apparatus, detachably mountable to an image forming apparatus main body for developing an electrostatic latent image formed on an image bearing member with a developer, the developing apparatus comprising: a developer container, a developer contained in the developer container; a developer carrying member for carrying the developer for developing the electrostatic latent image with the developer, the developer carrying member having a core electrode for rotatably supporting the developer carrying member; a developer supplying member provided in contact with the developer carrying member for supplying the developer to the developer carrying member, the developer supplying member having a surface foam layer in which the developer can enter and a core electrode for rotatably supporting the developer supplying member; a first contact electrode connectable to an alternating bias source provided in the image forming apparatus main body for applying an alternating bias to the core electrode of the developer carrying member or the core electrode of the developer supplying member; and a second contact electrode connectable to detecting means for detecting a capacitance between the core electrode of the developer carrying member and the core electrode of the developer supplying member when applying the alternating bias to the core electrode of the developer carrying member or the core electrode of the developer supplying member, wherein a surface aeration amount L in liter / minute of the developer supplying member satisfies a relation of 1.8 ≤ L when the surface aeration amount L is measured by: (i) inserting the developer supplying member into a measurement jig including a hollow cylinder having an inner diameter smaller by 1 mm than an outer diameter of the developer supplying member, and two through-holes each having a diameter of 10 mm in a side surface of the hollow cylinder, one through-hole being exposed to ambient air and the other through-hole being communicated with a flowmeter and a decompression pump, and (ii) measuring a value of the flowmeter when the decompression pump evacuates air from the measurement arrangement under the same exhaust condition as an exhaust condition in which a value of the flowmeter is 10.8 liters/minute in a state in which the developer supplying member is not inserted into the hollow cylinder, wherein a degree of compaction of the developer contained in the container is less than 30%. a developer container, a developer contained in the developer container; a developer carrying member for carrying the developer for developing the electrostatic latent image with the developer, the developer carrying member having a core electrode for rotatably supporting the developer carrying member; a developer supplying member provided in contact with the developer carrying member for supplying the developer to the developer carrying member, the developer supplying member having a surface foam layer in which the developer can enter and a core electrode for rotatably supporting the developer supplying member; a first contact electrode connectable to an alternating bias source provided in the image forming apparatus main body for applying an alternating bias to the core electrode of the developer carrying member or the core electrode of the developer supplying member; and a second contact electrode connectable to detecting means for detecting a capacitance between the core electrode of the developer carrying member and the core electrode of the developer supplying member when applying the alternating bias to the core electrode of the developer carrying member or the core electrode of the developer supplying member, wherein a surface aeration amount L in liter / minute of the developer supplying member satisfies a relation of 1.8 ≤ L when the surface aeration amount L is measured by: (i) inserting the developer supplying member into a measurement jig including a hollow cylinder having an inner diameter smaller by 1 mm than an outer diameter of the developer supplying member, and two through-holes each having a diameter of 10 mm in a side surface of the hollow cylinder, one through-hole being exposed to ambient air and the other through-hole being communicated with a flowmeter and a decompression pump, and (ii) measuring a value of the flowmeter when the decompression pump evacuates air from the measurement arrangement under the same exhaust condition as an exhaust condition in which a value of the flowmeter is 10.8 liters/minute in a state in which the developer supplying member is not inserted into the hollow cylinder, (i) inserting the developer supplying member into a measurement jig including a hollow cylinder having an inner diameter smaller by 1 mm than an outer diameter of the developer supplying member, and two through-holes each having a diameter of 10 mm in a side surface of the hollow cylinder, one through-hole being exposed to ambient air and the other through-hole being communicated with a flowmeter and a decompression pump, and (ii) measuring a value of the flowmeter when the decompression pump evacuates air from the measurement arrangement under the same exhaust condition as an exhaust condition in which a value of the flowmeter is 10.8 liters/minute in a state in which the developer supplying member is not inserted into the hollow cylinder, wherein a degree of compaction of the developer contained in the container is less than 30%.