Provided is an electrode-forming material for an electrochemical capacitor useful for forming an electrode of an electrochemical capacitor having a high storage capacity and a high energy density. The electrode-forming material for an electrochemical capacitor according to an embodiment of the present invention includes boron-doped nanodiamond (A) having a specific surface area of 110 m2/g or greater and an electrical conductivity at 20° C. of 5.0×10−3 S/cm or greater; and a metal oxide (B), and the content of the (B) is from 20 to 95 mass % with respect to the total content of the (A) and (B).