A thin film capacitor with high capacity and low leak current is provided. The thin film capacitor includes a nickel substrate with nickel (Ni) purity of 99.99 weight percent or above, and a dielectric layer and an electrode layer disposed in this order on the nickel substrate. The thin film capacitor is typically manufactured as follows. A precursor dielectric layer is formed on a nickel substrate with nickel purity of 99.99 weight percent or above, and is subjected to annealing to form a dielectric layer. The diffusion of impurities from the nickel substrate to the precursor dielectric layer during annealing is suppressed.