A device which can produce polarized rare gas further improved in polarization rate with the gas kept flowing, which has flat sheet surfaces facing each other via a gap, and which comprises, a flat-surface flow cell unit for allowing a mixture gas of rare gas and optically-pumping catalyst to flow in the gap there through in one direction thereof, a laser beam irradiation unit for applying a laser beam toward at least one of the flat sheet surfaces to apply an excitation light into the flat-surface flow cell unit, and a magnetic field application unit for allowing a magnetic line of force to pass through the laser beam-applied flat sheet surface perpendicularly or almost perpendicularly; and a method using this device.