Rail assembly

A rail assembly, comprising:

• an outer rail, a middle rail, an inner rail, and a retrieving unit, wherein the outer rail has an outer rail space for accommodating the middle rail, the inner rail and the retrieving unit;
• the middle rail slides in the outer rail space, and has a middle rail space for accommodating the inner rail;
• the inner rail accommodated in the middle rail, and sliding in the middle rail space;
• and
• the retrieving unit assembled on one end of the outer rail space, and comprises:
• a fixing part, disposed in the outer rail space, such that one end of the outer rail space is made into a closed end, the other end is made into an opened end;
• a sliding rail, formed by two sided slots of the outer rail at the opened end;
• a moving part, disposed in the outer rail space, and sliding along the sliding rail;
• a buckling mechanism, disposed on the moving part;
• at least one elastic part, disposed between the fixing part and the moving part;
• and
• a guiding part, disposed on the inner rail and corresponding to the buckling mechanism;
• wherein the moving part slides along the sliding rail in the outer rail space at the opened end, the movement of the moving part are not restricted by a length of the fixing part.