A porous metal thin film formed from aluminum has a film structure in which domains having an average diameter of 200 nm or more, and 500 nm or less and being formed through aggregation of a plurality of grains having an average grain diameter of 50 nm or more, and 160 nm or less are distributed discretely at an average distance of 5 nm or more, and 40 nm or less, wherein the area occupied by the above-described domains is 60% or more, and 90% or less in a cross-section in any direction of the porous metal thin film.