A polishing apparatus has an automated endpoint detection device to determine if an endpoint of polishing has been reached without removing the wafer from a top ring of the polishing apparatus. When a pre-determined inspection time is reached in a process of polishing, the wafer is moved laterally along the turntable and the current surface condition of the wafer is determined by comparing the current surface condition with an initial surface condition, having an oxide film for example, determined from surface reflection measurement data carried out opto-electronically on the wafer before polishing. The endpoint detection device can be used to remove the surface oxide film so that the apex of the underlying device elements are just exposed. By eliminating the need for removing the wafer from the top ring for inspection, the cost of handling the wafer for polishing is reduced significantly, and enables reduction in the cost of manufactured devices. The endpoint determination device is applicable to any type of flat objects, such as LCD panels, requiring a high degree of polishing precision.