An outer wall structure of the invention includes an outer wall mounting member composed of a supporting plate and a plurality of securing members. The supporting plate includes a plate body and a positioning portion. With this outer wall structure, the plate body is fixed to a horizontal furring strip member and a frame member in an upside portion and a downside portion of a sash body of a window sash at a second distance away from an outer surface of the sash body. The securing members are fixed to the plate body at a third distance away from the outer surface of the sash body. In this outer wall structure, the position at the second distance is farther away from the outer face than the position at a distance from the outer surface of the sash body to a distal end portion of a flange of the sash body.