A calibration method for calibrating a measurement device for measuring a concentration of a gas dissolved in a liquid includes varying the concentration of the gas dissolved in the liquid, and predetermining, as a reference concentration, a concentration of the gas at which an intensity of luminescence produced when the liquid is irradiated with ultrasonic waves shows a peak. The liquid is illuminated with ultrasonic waves while varying the concentration of the gas in the liquid and a measured value is measured, using the measurement device, as a concentration of the gas in the liquid when the intensity of the luminescence shows a peak. The measurement device is calibrated based on the measured value and the reference concentration.