A developing device including a first frame including a first welding surface and a second frame including a second welding surface, wherein the first frame and the second frame are welded so that the first welding surface and the second welding surface are opposite to each other, and wherein the developing device further includes: a seal member that is adhered to a first adhesion surface of the first frame and a second adhesion surface of the second frame, wherein the seal member covers a first side end portion from a first side in an orthogonal direction at an opposite part, where the first welding surface and the second welding surface are disposed opposite one another; and a filling agent that is filled between the seal member and the first side end portion in the orthogonal direction at the opposite part.