A developing device includes: a developing roller that supplies toner so as to develop an electrostatic latent image into a toner image; and a seal member that prevents toner from leaking from end portions in the axial direction of the developing roller to the outside and the developing device is characterized by a structure in that the developing roller includes a sheet member disposed so as to cover the surface of the end portions in the axial direction of the developing roller, and the sheet member has no seam in the circumferential direction, and has a surface roughness that is smaller than that of the developing roller, or has a surface hardness that is higher than that of a synthetic resin as a base material of the toner.