The object of the present invention is to obtain a low profile electrolytic copper foil with a low surface roughness at the rough surface side (opposite side from the glossy side) in the electrolytic copper foil manufacture using a cathode drum and, particularly, to obtain an electrolytic copper foil with excellent elongation and tensile strength that permits fine patterning. Another object is to obtain a copper electrolytic solution that allows uniform copper plating without pinholes on a 2-layer flexible substrate. This copper electrolytic solution contains, as an additive, a compound having the specific skeleton represented by General Formula (1) below which is obtained by an addition reaction in which water is added to a compound having in a molecule one or more epoxy groups: wherein A is an epoxy compound residue and n is an integer of 1 or more.