Disclosed herein is a lamp cooling device for cooling a lamp including a light emission source for emitting light, a front transparent plate, a reflector for reflecting light emitted by the light emission source toward the front transparent plate, the light emission source being disposed in an intralamp space surrounded by the front transparent plate and the reflector, said lamp cooling device including: a duct having joint ports defined in respective opposite ends thereof and communicating with said intralamp space, said duct having a continuously extending portion between said opposite ends which is disposed in a space outside of said intralamp space, for circulating a gas through said duct and said intralamp space in isolated relation to the space outside of said intralamp space.