In an image-forming device including an image-carrying member, a developer-carrying member, and a casing having an inner space in which developer is accommodated and the developer-carrying member is supported, both a pushing force and a separating force are not applied to the casing so that the thickness of the casing does not need to be increased. The casing is formed with a pair of first protruding parts each having an end that protrudes outward along the axial direction of the developer-carrying member, and a pair of second protruding parts each having an end that protrudes farther outward than the corresponding end of the first protruding part. The first protruding parts serve as operating parts operated by a pressing member, and the second protruding parts serve as operating parts operated by a separating member.