A stage apparatus includes X- and Y-axis laser interferometers each of which measures the position a stage, a wavelength compensator which compensates for the wavelength change of a laser beam from each of the X- and Y-axis laser interferometers, a fan duct which is connected to a thermoregulator for supplying a temperature-controlled gas and supplies the temperature-controlled gas to the optical axes of the X- and Y-axis laser interferometers, and a fan duct which is connected to the thermoregulator and supplies the temperature-controlled gas to the wavelength compensator. The time necessary for supplying the temperature-controlled gas from the thermoregulator to the optical axes of the X- and Y-axis laser interferometers through the fan duct is equal to the time necessary for supplying the temperature-controlled gas from the thermoregulator to the wavelength compensator through the fan duct.