Polishing apparatus and polishing method

A polishing apparatus which can measure a film thickness with high accuracy without affecting a polishing rate of a wafer is disclosed. The polishing apparatus includes: a polishing head configured to press a wafer against a polishing pad; an illuminating fiber having a distal end disposed in a flow passage formed in the polishing table; a spectrometer configured to resolve reflected light from the wafer in accordance with wavelength and measure an intensity of the reflected light at each of the wavelengths; a light-receiving fiber having a distal end disposed in the flow passage; a liquid supply line communicating with the flow passage; a gas supply line communicating with the flow passage; a liquid supply valve attached to the liquid supply line; a gas supply valve attached to the gas supply line; and an operation controller configured to control operations of the liquid supply valve and the gas supply valve.