A polishing apparatus is used for polishing a substrate such as a semiconductor wafer to a flat mirror finish. The polishing apparatus includes a polishing table having a polishing surface, a top ring configured to hold and press the substrate against the polishing surface, a top ring shaft configured to lift and lower the top ring, and an elongation detecting device configured to detect an elongation of the top ring shaft. The polishing apparatus further includes a controller configured to set a vertical position of the top ring at the time of polishing, and control a lifting and lowering mechanism to lower the top ring to a preset polishing position as the set vertical position. The controller corrects the preset polishing position based on the elongation of the top ring shaft which has been detected by the elongation detecting device.