An electronic component mounting structure includes a three-dimensional substrate having a three-dimensional shape and including a hollow portion formed on at least one of side surfaces of the three-dimensional substrate, and an electronic component mounted on a bottom face of the hollow portion. The three-dimensional substrate includes an opening portion on a side surface different from a side surface on which the hollow portion is formed for allowing observation of a connection portion between the bottom face of the hollow portion and the electronic component from an outer periphery side of the three-dimensional substrate.