A developing device comprising: a rotatable developing sleeve configured to carry and feed a developer including toner and a magnetic carrier toward a developing region (Da) where the developer contacts an image bearing member and where an electrostatic latent image formed on the image bearing member is developed with the developer; and a magnetic field generating portion provided inside said developing sleeve and having a developing magnetic pole, the developing magnetic pole being disposed opposed to a closest position of said image bearing member to said developing sleeve, characterized in that a ratio of an 80 %-value-width of magnetic flux density (Br) of the developing magnetic pole with respect to a normal direction of said developing sleeve to a half peak width of the magnetic flux density (Br) of the developing magnetic pole with respect to the normal direction is 0.65 or more, wherein a magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to an upstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve is larger than a magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve at a center portion of the developing region (Da) with respect to the rotational direction of said developing sleeve, a peak position of the magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to the upstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve being positioned outside of the developing region (Da) with respect to the rotational direction of said developing sleeve, and wherein a magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to a downstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve is larger than the magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve at the center portion of the developing region (Da) with respect to the rotational direction of said developing sleeve, a peak position of the magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to the downstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve being positioned outside of the developing region (Da) with respect to the rotational direction of said developing sleeve. a rotatable developing sleeve configured to carry and feed a developer including toner and a magnetic carrier toward a developing region (Da) where the developer contacts an image bearing member and where an electrostatic latent image formed on the image bearing member is developed with the developer; and a magnetic field generating portion provided inside said developing sleeve and having a developing magnetic pole, the developing magnetic pole being disposed opposed to a closest position of said image bearing member to said developing sleeve, characterized in that a ratio of an 80 %-value-width of magnetic flux density (Br) of the developing magnetic pole with respect to a normal direction of said developing sleeve to a half peak width of the magnetic flux density (Br) of the developing magnetic pole with respect to the normal direction is 0.65 or more, wherein a magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to an upstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve is larger than a magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve at a center portion of the developing region (Da) with respect to the rotational direction of said developing sleeve, a peak position of the magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to the upstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve being positioned outside of the developing region (Da) with respect to the rotational direction of said developing sleeve, and wherein a magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to a downstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve is larger than the magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve at the center portion of the developing region (Da) with respect to the rotational direction of said developing sleeve, a peak position of the magnetic force (Fr) of the developing magnetic pole in the normal direction of said developing sleeve proximate to the downstream end portion of the developing region (Da) with respect to the rotational direction of said developing sleeve being positioned outside of the developing region (Da) with respect to the rotational direction of said developing sleeve.