A developing device, comprising: a housing having an opening in a wall thereof; a developing roller rotatably arranged within the housing to rotate in a rotation direction (Jl) about a roller axial direction (Vg) of the development roller, the developing roller including a shaft, a plurality of magnetic pole sections (N1, S1, N2, N3, S2), and a sleeve; and a gap forming member forms a first gap with the developing roller and a second gap between the gap forming member and the housing, the gap forming member facing the developing roller across the first gap and facing the housing across the second gap wherein: the developing roller faces a photoconductive drum through the opening, the shaft extends in the roller axial direction (Vg), both ends of the shaft being fixed to the housing, the plurality of the magnetic pole sections (N1, S1, N2, N3, S2) are fixed at fixed positions at intervals in a circumferential direction of the shaft, the sleeve is formed into a cylindrical shape including the shaft and the plurality of the magnetic pole sections (N1, S1, N2, N3, S2) therein, the sleeve being rotatable in the rotation direction (Jl) with respect to the magnetic pole sections (N1, S1, N2, N3, S2); wherein the developing device further comprises: a blocking member arranged in the first gap, and a guide section configured to guide airflow passing through the second gap in a direction toward the developing roller; wherein: a first opening and a second opening are arranged between the housing and the gap forming member, the first opening is formed at a downstream side of the roller rotation direction (Jl) with respect to the gap forming member, the second opening communicates with the first opening through the second gap, the second opening is formed at a upstream side of the roller rotation direction (Jl) with respect to the gap forming member, and the guide section is configured to guide the airflow discharged from the second gap through the second opening between the blocking member and the developing roller, characterized by the blocking member being formed into a loop shape and supported by the gap forming member. a housing having an opening in a wall thereof; a developing roller rotatably arranged within the housing to rotate in a rotation direction (Jl) about a roller axial direction (Vg) of the development roller, the developing roller including a shaft, a plurality of magnetic pole sections (N1, S1, N2, N3, S2), and a sleeve; and a gap forming member forms a first gap with the developing roller and a second gap between the gap forming member and the housing, the gap forming member facing the developing roller across the first gap and facing the housing across the second gap wherein: the developing roller faces a photoconductive drum through the opening, the shaft extends in the roller axial direction (Vg), both ends of the shaft being fixed to the housing, the plurality of the magnetic pole sections (N1, S1, N2, N3, S2) are fixed at fixed positions at intervals in a circumferential direction of the shaft, the sleeve is formed into a cylindrical shape including the shaft and the plurality of the magnetic pole sections (N1, S1, N2, N3, S2) therein, the sleeve being rotatable in the rotation direction (Jl) with respect to the magnetic pole sections (N1, S1, N2, N3, S2); the developing roller faces a photoconductive drum through the opening, the shaft extends in the roller axial direction (Vg), both ends of the shaft being fixed to the housing, the plurality of the magnetic pole sections (N1, S1, N2, N3, S2) are fixed at fixed positions at intervals in a circumferential direction of the shaft, the sleeve is formed into a cylindrical shape including the shaft and the plurality of the magnetic pole sections (N1, S1, N2, N3, S2) therein, the sleeve being rotatable in the rotation direction (Jl) with respect to the magnetic pole sections (N1, S1, N2, N3, S2); a blocking member arranged in the first gap, and a guide section configured to guide airflow passing through the second gap in a direction toward the developing roller; wherein: a first opening and a second opening are arranged between the housing and the gap forming member, the first opening is formed at a downstream side of the roller rotation direction (Jl) with respect to the gap forming member, the second opening communicates with the first opening through the second gap, the second opening is formed at a upstream side of the roller rotation direction (Jl) with respect to the gap forming member, and the guide section is configured to guide the airflow discharged from the second gap through the second opening between the blocking member and the developing roller, characterized by the blocking member being formed into a loop shape and supported by the gap forming member. a first opening and a second opening are arranged between the housing and the gap forming member, the first opening is formed at a downstream side of the roller rotation direction (Jl) with respect to the gap forming member, the second opening communicates with the first opening through the second gap, the second opening is formed at a upstream side of the roller rotation direction (Jl) with respect to the gap forming member, and the guide section is configured to guide the airflow discharged from the second gap through the second opening between the blocking member and the developing roller, characterized by the blocking member being formed into a loop shape and supported by the gap forming member.