Considering that no heat-emitting illumination should be installed for the public exhibition of a stone chamber, the author tried to use an optical glass fiber light pipe as the illumination source in the stone chamber in the Torazuka tumulus, Ibaraki prefecture. The stone chamber was closed with a double glazing which separated the chamber from a reinforced concrete observation room. The optical glass fiber light pipe was installed in the observation room. The light pipe is 3 meters long and is connected to the lamp house which contains a light source including a halogen lamp, reflection mirror, fan and heat absorbing filter. The light pipe is inserted 1.5m into the chamber to illuminate the wall paintings. The illuminance on the wall surface was 20 luxes at the farthest point, 3m, from the tip of the pipe. There was no obstruction to observe the painting in the chamber at this illuminance and no internal heat build-up was recorded during the eight hours of daily public exhibition. -- AATA