Straight, nano-scale-order amorphous carbon tubes having a long-term stable ability for storing various kinds of gases and being stable in shape, and a novel process for producing said carbon tubes with high purity, high yield and high mass-productivity are provided. The amorphous nano-scale carbon tubes are prepared by subjecting a heat-decomposable resin having a decomposition temperature of 200 to 900 C. to an excitation treatment in the presence of a metal powder and/or a metal salt, or by subjecting a carbon material containing —CC— and/or C to a heat-treatment at 3000 C. or lower.