A developing apparatus comprising at least: a developer for developing an electrostatic latent image formed on a photosensitive drum; a developer bearing member for bearing and conveying the developer; and a developer layer thickness-regulating unit placed close to the developer bearing member so as to regulate an amount of the developer borne and conveyed by the developer bearing member, wherein: the developer is a negatively chargeable, one-component, magnetic toner, and comprises magnetic toner particles each comprising at least a binder resin and magnetic iron oxide particle, the developer has a saturation magnetization of 20 Am 2 /kg or more and 40 Am 2 /kg or less in a magnetic field of 795.8 kA/m, and has a weight-average particle diameter (D 4) of 4.0 μm or more and 8.0 μm or less, wherein a ratio X of an amount of Fe(2+) to a total amount of Fe in the magnetic iron oxide particle is 34% or more and 50% or less, the total amount of Fe being an amount of Fe element when the magnetic iron oxide particle is dissolved so that an Fe element-dissolving ratio reaches 10 mass%; the developer bearing member comprises at least a substrate, a resin layer as a surface layer formed on the substrate, and a magnetic member provided in the substrate, and the resin layer has the developer triboelectrically-charged negatively, and contains a binder resin having in its structure at least one selected from the group consisting of a -NH 2 group, a =NH group, and a -NH- bond, a quaternary ammonium salt for reducing a property of imparting negative triboelectric charges to the developer, graphitized particles each having a degree of graphitization p of 0.22 or more and 0.75 or less, and conductive, spherical carbon particles having a volume-average particle diameter of 4.0 μm to 8.0 μm as particles for providing a surface of the resin layer with irregularities, wherein when a square region of 0.50 mm in side on the surface of the developer bearing member is equally divided with 725 straight lines which are parallel to one side of the square region, and other 725 straight lines intersecting therewith at right angle, the whole area of the developer bearing member on which the developer is borne has a plurality of independent protrusions whose heights exceeds D 4 /4 with reference to an average of three-dimensional heights measured at intersections of the 725 straight lines and the other 725 straight lines, wherein the sum of areas of the protrusions at a height of D 4 /4 is 5% or more and 30% or less of the region, arithmetic average roughness Ra determined from only the protrusions is 0.25 μm or more and 0.55 μm or less, and arithmetic average roughness Ra determined from area other than the protrusions is 0.65 μm or more and 1.20 μm or less. a developer for developing an electrostatic latent image formed on a photosensitive drum; a developer bearing member for bearing and conveying the developer; and a developer layer thickness-regulating unit placed close to the developer bearing member so as to regulate an amount of the developer borne and conveyed by the developer bearing member, the developer is a negatively chargeable, one-component, magnetic toner, and comprises magnetic toner particles each comprising at least a binder resin and magnetic iron oxide particle, the developer has a saturation magnetization of 20 Am 2 /kg or more and 40 Am 2 /kg or less in a magnetic field of 795.8 kA/m, and has a weight-average particle diameter (D 4) of 4.0 μm or more and 8.0 μm or less, wherein a ratio X of an amount of Fe(2+) to a total amount of Fe in the magnetic iron oxide particle is 34% or more and 50% or less, the total amount of Fe being an amount of Fe element when the magnetic iron oxide particle is dissolved so that an Fe element-dissolving ratio reaches 10 mass%; the developer bearing member comprises at least a substrate, a resin layer as a surface layer formed on the substrate, and a magnetic member provided in the substrate, and the resin layer has the developer triboelectrically-charged negatively, and contains a binder resin having in its structure at least one selected from the group consisting of a -NH 2 group, a =NH group, and a -NH- bond, a quaternary ammonium salt for reducing a property of imparting negative triboelectric charges to the developer, graphitized particles each having a degree of graphitization p of 0.22 or more and 0.75 or less, and conductive, spherical carbon particles having a volume-average particle diameter of 4.0 μm to 8.0 μm as particles for providing a surface of the resin layer with irregularities, wherein