A substrate processing apparatus fills a metal such as copper or the like in fine interconnection patterns or trenches defined in a semiconductor substrate. The substrate processing apparatus has a loading/unloading unit for placing a substrate cassette to allow a substrate to be loaded and unloaded, a substrate treating unit for treating a substrate, and a transfer robot for transferring a substrate between the loading/unloading unit and the substrate treating unit. The loading/unloading unit, the substrate treating unit, and the transfer robot are installed in a single facility. The loading/unloading unit has a rotary table which is horizontally rotatable for positioning the substrate cassette in a position to detect the substrate cassette placed in the loading/unloading unit and to remove the substrate from the substrate cassette with the transfer robot.