A development device comprising: a development casing for containing developer; a developer bearer disposed facing a latent image bearer to carry by rotation developer to a development range facing the latent image bearer; a first developer conveyance member which includes a rotary shaft and a spiral-shaped blade around the rotary shaft to supply developer to the developer bearer while transporting the developer axially by rotation of the first developer conveyance member; a second developer conveyance member which includes a rotary shaft and a spiral-shaped blade around the rotary shaft to transport developer axially by rotation of the second developer conveyance member; a supply channel in which the first developer conveyance member is provided; a collecting channel via which developer received from a downstream end portion of the supply channel is forwarded by the second developer conveyance member to an upstream end portion of the supply channel; and a partition separating, at least partly, the supply channel from the collecting channel, wherein the supply channel includes: a conveyance area in which the first developer conveyance member exerts conveyance force on developer, and a buffer area adjacent to the conveyance area in a direction perpendicular to an axial direction of the first developer conveyance member to temporarily retain developer supplied to the developer bearer, the buffer area in which the conveyance force from the first developer conveyance member is not directly exerted on developer, the buffer area is positioned midway in the developer conveyance direction inside the supply channel, characterized in that an inner wall of the development casing is formed as an upstream end face defining an upstream end of the buffer area and is inclined relative to the axial direction of the first developer conveyance member to draw away from the conveyance area downstream in the developer conveyance direction, wherein the joint between the conveyance area and the buffer area is tapered in order to facilitate the flow of developer. a development casing for containing developer; a developer bearer disposed facing a latent image bearer to carry by rotation developer to a development range facing the latent image bearer; a first developer conveyance member which includes a rotary shaft and a spiral-shaped blade around the rotary shaft to supply developer to the developer bearer while transporting the developer axially by rotation of the first developer conveyance member; a second developer conveyance member which includes a rotary shaft and a spiral-shaped blade around the rotary shaft to transport developer axially by rotation of the second developer conveyance member; a supply channel in which the first developer conveyance member is provided; a collecting channel via which developer received from a downstream end portion of the supply channel is forwarded by the second developer conveyance member to an upstream end portion of the supply channel; and a partition separating, at least partly, the supply channel from the collecting channel, wherein the supply channel includes: a conveyance area in which the first developer conveyance member exerts conveyance force on developer, and a buffer area adjacent to the conveyance area in a direction perpendicular to an axial direction of the first developer conveyance member to temporarily retain developer supplied to the developer bearer, the buffer area in which the conveyance force from the first developer conveyance member is not directly exerted on developer, the buffer area is positioned midway in the developer conveyance direction inside the supply channel, characterized in that an inner wall of the development casing is formed as an upstream end face defining an upstream end of the buffer area and is inclined relative to the axial direction of the first developer conveyance member to draw away from the conveyance area downstream in the developer conveyance direction, wherein the joint between the conveyance area and the buffer area is tapered in order to facilitate the flow of developer. a conveyance area in which the first developer conveyance member exerts conveyance force on developer, and a buffer area adjacent to the conveyance area in a direction perpendicular to an axial direction of the first developer conveyance member to temporarily retain developer supplied to the developer bearer, the buffer area in which the conveyance force from the first developer conveyance member is not directly exerted on developer, the buffer area is positioned midway in the developer conveyance direction inside the supply channel, characterized in that an inner wall of the development casing is formed as an upstream end face defining an upstream end of the buffer area and is inclined relative to the axial direction of the first developer conveyance member to draw away from the conveyance area downstream in the developer conveyance direction, wherein the joint between the conveyance area and the buffer area is tapered in order to facilitate the flow of developer.