A first cartridge and a second cartridge are detachably mounted in a housing of the image-forming device. The first cartridge is formed thicker than the second cartridge in a thickness direction orthogonal to a mounting direction of the first and second cartridges. The housing has a cartridge-accommodating section that accommodates the first and second cartridges. The cartridge-accommodating section includes first and second accommodating sections that are disposed continuously along the mounting direction and that are partly displaced with respect to each other in the thickness direction. The second accommodating section is disposed upstream of the first accommodating section with respect to the mounting direction and is formed thicker than the first cartridge and thinner than both the first and second cartridges together when the first and second cartridges are accommodated in the cartridge-accommodating section. The first accommodating section is formed thicker than the first and second cartridges together when the first and second cartridges are accommodated in the cartridge-accommodating section.