The invention is to provide a slim optical disk drive, which includes several braces extended from two edges of an upper cover. Each brace extends two fixing parts with a buckle hole from the center and the bottom. The upper and lower surface of each guide of a guide unit is concaved to form position recesses with a wedge. The guide places between two fixing parts, the fixing part and engages in the position recess, and the wedge is inserted into the buckle hole. A tray covered a base plate on bottom is supported by two bars sliding in two guides.