The present invention provides: a chemical conversion body with which a porous electrolytic capacitor and device exhibiting high bonding strength and high capacitance can be produced; and a production method therefor. This capacitor is provided with: a chemical conversion body which serves as a positive electrode of the capacitor, which has, on a surface thereof, a dielectric layer, and which comprises niobium and a compound including a metal other than niobium, said chemical conversion body being characterized in that the metal other than niobium is distributed so as to surround the periphery of the niobium; and a negative electrode above the chemical conversion body and the dielectric layer on the surface of the chemical conversion body. The chemical conversion body can be obtained by mixing niobium hydride and the compound including a metal other than niobium to obtain a mixed substance, heat treating the mixed substance at a temperature higher than the diffusion start temperature of the compound including the metal other than niobium to obtain a niobium granulated substance, sintering the niobium granulated substance to obtain a sintered body, and subjecting the sintered body to electrolytic oxidation to form the dielectric layer upon a surface thereof.