A developing device used for forming a toner image by developing the electrostatic latent image on an electrostatic latent image carrier in an image forming device, comprises a developer carrier roller which is rotationally driven, and a toner thin layer forming member which is brought into contact with the developer carrier roller, wherein the developer carrier roller is formed in the shape of an inverted crown which is concave at the central portion in the direction of the rotation axis, and a starting point of the shape of the inverted crown is positioned further outside in the direction of the rotation axis than toner thin layer region formed by the toner thin layer forming member.