It is intended to highly efficiently produce a high-density brush-shaped carbon nanostructure useful in the production of CNT assembly, such as rope-shaped CNTs, and provide a catalyst body for production of brush-shaped carbon nanostructure that enables the production. The catalyst body for production of brush-shaped carbon nanostructure is one comprising a substrate (32), an aggregation suppressive layer (34) superimposed on a surface thereof and a catalyst layer superimposed on the aggregation suppressive layer (34). The catalyst layer is a catalyst particle layer (44) consisting of metallic catalyst particles (42) composed mainly of a catalytic metal. The metallic catalyst particles (42) have an average particle diameter, D, satisfying the relationship 0.5 nm≦D≦80 nm, and individual particles of the metallic catalyst particles (42) have a diameter, d, falling within the range of the above average particle diameter (D). Further, there are disclosed a process for producing the catalyst body, a brush-shaped carbon nanostructure and a process for producing the same.