A developing device, used in an image forming device where a developer supported on a developer supporter is thinned by a thinning member, and after being thinned, the developer is adhered to develop a latent image on an image supporter. An adjacent member (a developer scattering blocking member) is disposed at a position adjacent to the thinning member's downstream side in the developer supporter's moving direction, and the adjacent member's thinning member side of the opposite surface that is opposite to the developer supporter and the tip of the thinning member are disposed with an equal distance from the developer supporter. The opposite surface is gradually separated from the developer supporter at the downstream side of the developer supporter's moving direction.