The purpose of the present invention is to provide a method and an apparatus for producing carbon nanotube aggregates to improve the contact efficiency between a source gas and catalysts, thereby enabling the efficient production of high-quality CNT aggregates. A method for producing carbon nanotube aggregates according to the disclosure is a method including a growth step of growing the carbon nanotube aggregates on substrates with catalysts on surfaces. In the growth step, a source gas supply step of forming a substrate layer by stacking the substrates at a lower portion of a growth furnace configured to perform the growth step, and supplying a source gas to the substrate layer through a plurality of gas injection ports arranged at the lower portion of the growth furnace, and an in-growth furnace stir and conveyance step of mechanically stirring and/or conveying the substrate layer are performed at least in part in an overlapping manner.