Image-reading device and carriage drive structure for image-reading device

A carriage drive structure for an image-reading device that includes a platen glass for supporting a document, a light source for irradiating light onto the document through the platen glass, a photoelectric transfer device for acquiring image information from the light reflected from the document, and a reading optical system for guiding the reflected light to the photoelectric transfer device, comprising:

• a housing that includes at least three walls;
• a carriage supported in said housing and that includes opposite ends adjacent two of said at least three walls, said carriage supporting at least part of the reading optical system;
• and
• an endless circulatory movable body that is supported in said housing, that is movable in a circulatory manner, and that includes two portions that extend along each of said three walls and are connected to opposite ends of said carriage so that said two portions move in different directions along each of said three walls in order to drive said carriage in a single direction upon movement of said endless circulatory movable body in a circulatory manner.