A carbon nanotube aggregate includes a plurality of carbon nanotubes, a metal compound, and an oxide of the metal compound. The metal compound is contained in a space inside of each of the carbon nanotubes and/or in a space defined between the plurality of carbon nanotubes. When the metal compound is added inside the carbon nanotube aggregate, the metal compound is oxidized by reacting with oxygen or the like during or after a production process of the CNT aggregate, and the oxide is formed in the opening of the space to which the metal compound is added, so that the metal compound is capped with the oxide. Since the metal compound inside the CNT aggregate is shielded from the atmosphere, separation of the metal compound and reaction between the metal compound and oxygen and water in the atmosphere are suppressed, increasing heat resistance of the carbon nanotube aggregate.