There is provided a planar structural body 1 comprising a fibrous carbon nanohorn aggregate 2 in which a plurality of single-walled carbon nanohorns are aggregated in a fibrous state, and particularly the planar structural body in which a globular carbon nanohorn aggregate 3 is mixed is used. The planar structural body comprising such a fibrous carbon nanohorn aggregate can be used for electrode materials for lithium ion batteries, fuel cells, capacitors, electrochemical actuators, air cells, solar cells, and the like, and can be used also for electromagnetic shields, thermoconductive sheets, heat-dissipating sheets, protecting sheets, filters and absorbing materials.