A polishing apparatus polishes a surface of a substrate by pressing the substrate against a polishing pad on a polishing table. The polishing apparatus includes a polishing liquid supply nozzle for supplying a polishing liquid onto the polishing pad, a polishing liquid storage mechanism disposed on the polishing pad for storing the polishing liquid on the polishing pad by damming the polishing liquid, and a polishing liquid sensor for measuring a physical quantity representing the freshness of the polishing liquid stored by the polishing liquid storage mechanism. The polishing apparatus further includes a freshness measuring instrument for calculating the freshness of the stored polishing liquid from the physical quantity measured by the polishing liquid sensor, and a freshness controller for controlling supply conditions of the polishing liquid or storage state of the polishing liquid, based on the freshness of the polishing liquid that is determined by the freshness measuring instrument.