This invention provides an aligned single-walled CNT aggregate comprising a substrate, fine particles of iron catalyst with a density of 1×1011 to 1×1014/cm2 disposed on an alumina co-catalyst above the substrate, and a plurality of single-walled CNTs grown from the fine particles of the iron catalyst, in which the plurality of single-walled CNTs have a specific surface area of 600 m2/g to 2600 m2/g, and a weight density from 0.002 g/cm3 to 0.2 g/cm3, and the alignment degree which satisfies a few of specific conditions. This invention also provides a bulk aligned single-walled carbon nanotube aggregate and a powdered aligned single-walled carbon nanotube aggregate.