A developing device, comprising: a case main body comprising an opening; a developing roller coupled with the case main body at a position facing the opening, the developing roller capable of rotating and supporting developer housed in the case main body; an adjustment member coupled with the case main body and extending along a rotation axis direction of the developing roller, the adjustment member adjusting the thickness of the developer supported by the developing roller; and a side seal member (150,152), wherein the case main body comprises a first area facing a peripheral surface of the developing roller, the adjustment member comprises a second area facing the peripheral surface of the developing roller, the first area and the second area are aligned along a rotation direction of the developing roller, the side seal member (150,152) comprises a first seal member mounted on the first area and making contact with the peripheral surface of the developing roller, and a second seal member mounted on the second area and making contact with the peripheral surface of the developing roller, and the first seal member and the second seal member are configured separately and make contact with one another, characterized in that the first seal member comprises a first elastic member mounted on the first area, and a first contact member mounted on an upper surface of the first elastic member, an upper surface of the first contact member making contact with the peripheral surface of the developing roller, the second seal member comprises a second elastic member mounted on the second area, and a second contact member mounted on an upper surface of the second elastic member, a part of the second seal member overlaps with the upper surface of the first contact member of the first seal member, the part of the second seal member including a part of the second elastic member and a part of the second contact member, and both the part of the second elastic member and the part of the second contact member are located between the peripheral surface of the developing roller and the upper surface of the first contact member. a case main body comprising an opening; a developing roller coupled with the case main body at a position facing the opening, the developing roller capable of rotating and supporting developer housed in the case main body; an adjustment member coupled with the case main body and extending along a rotation axis direction of the developing roller, the adjustment member adjusting the thickness of the developer supported by the developing roller; and a side seal member (150,152), wherein the case main body comprises a first area facing a peripheral surface of the developing roller, the adjustment member comprises a second area facing the peripheral surface of the developing roller, the first area and the second area are aligned along a rotation direction of the developing roller, the side seal member (150,152) comprises a first seal member mounted on the first area and making contact with the peripheral surface of the developing roller, and a second seal member mounted on the second area and making contact with the peripheral surface of the developing roller, and the first seal member and the second seal member are configured separately and make contact with one another, characterized in that the first seal member comprises a first elastic member mounted on the first area, and a first contact member mounted on an upper surface of the first elastic member, an upper surface of the first contact member making contact with the peripheral surface of the developing roller, the second seal member comprises a second elastic member mounted on the second area, and a second contact member mounted on an upper surface of the second elastic member, a part of the second seal member overlaps with the upper surface of the first contact member of the first seal member, the part of the second seal member including a part of the second elastic member and a part of the second contact member, and both the part of the second elastic member and the part of the second contact member are located between the peripheral surface of the developing roller and the upper surface of the first contact member.