Disclosed is a method for producing ionomer-coated, catalyst-supporting carbon nanotubes, the method comprising: a step of preparing catalyst-supporting carbon nanotubes on at least one surface of a substrate; a step of preparing a first ionomer solution; an ionomer coating step of bringing the catalyst-supporting carbon nanotubes into contact with the first ionomer solution and coating the catalyst-supporting carbon nanotubes with the ionomer; and a drying step of drying the ionomer-coated, catalyst-supporting carbon nanotubes, wherein the method comprises an ionomer removal step in which, when the ionomer that is unevenly attached in a thickness direction of a layer comprising the ionomer-coated, catalyst-supporting carbon nanotubes, the ionomer that is relatively largely found in and attached to the tip end of the carbon nanotubes rather than other parts thereof, is removed after the ionomer coating step and before the drying step.