Image-forming device and belt unit

An image-forming device, comprising:

• a housing defining a linear insertion/removal path and defining an installation position on the linear insertion/removal path, an insertion direction and a removal direction being defined along the linear insertion/removal path as opposed to each other;
• at least one photosensitive member that is mounted in the housing and that forms a developer image thereon;
• and
• a belt unit that is detachably mounted in the housing, the belt unit being movable along the linear insertion/removal path, the belt unit moving to the installation position along the linear insertion/removal path in the insertion direction when the belt unit is mounted in the housing, the belt unit moving from the installation position along the linear insertion/removal path in the removal direction to be detached from the housing,
• the belt unit comprising:
• a plurality of rollers;
• and
• an endless belt that is supported by the plurality of rollers, the endless belt being capable of moving circumferentially around the plurality of rollers, a surface of the endless belt contacting a surface of the at least one photosensitive member when the belt unit is located in the installation position, the endless belt moving in a belt-moving direction at a contact position where the endless belt contacts each photosensitive member, the belt-moving direction being angularly shifted from the removal direction to allow the surface of the endless belt to separate from each photosensitive member when the belt unit starts moving in the removal direction from the installation position.