An insulated flat conductive wire having a high aspect ratio, comprising: a flat conductive wire having an aspect ratio a/b of 12 or more, wherein the aspect ratio is a ratio of a length a of a long side of a rectangular cross-section to a length b of a short side thereof; and an insulating film which consists of a polyamide-imide resin and coats the flat conductive wire, characterized in that a cross-sectional area of the flat conductive wire is set so that a diameter of a round wire having the same cross-sectional area as the rectangular cross-section of the flat conductive wire becomes 0.5 mm to 4.5 mm, the polyamide-imide resin has a number average molecular weight Mn of 2.0×10 4 to 4.0×10 4, wherein the number average molecular weight Mn is determined by gel permeation chromatography using standard polystyrene as described in the description, and the insulating film has a film thickness t1 of 10 μm or more at a center portion of the long side of the rectangular cross-section, and the insulating film has a film thickness ratio t1/t2 of 0.98 to 1.35, and wherein the film thickness ratio t1/t2 is a ratio of the film thickness t1 at the center portion of the long side to a film thickness t2 at an edge portion of the long side of the rectangular cross-section, wherein the film thickness t1 at the center portion of the long side is an average value of two locations at an upper side and a lower side in the center portion of the long side, the film thickness t2 is an average value of four locations at upper sides and lower sides in both edge portions of the long side, and the film thickness t2 at the edge portion of the long side refers to the thickest part where roundness disappears in the edge portion of the insulating film and the long side of the flat conductive wire and a surface of the insulating film begin to be parallel to each other. a flat conductive wire having an aspect ratio a/b of 12 or more, wherein the aspect ratio is a ratio of a length a of a long side of a rectangular cross-section to a length b of a short side thereof; and an insulating film which consists of a polyamide-imide resin and coats the flat conductive wire, characterized in that a cross-sectional area of the flat conductive wire is set so that a diameter of a round wire having the same cross-sectional area as the rectangular cross-section of the flat conductive wire becomes 0.5 mm to 4.5 mm, the polyamide-imide resin has a number average molecular weight Mn of 2.0×10 4 to 4.0×10 4, wherein the number average molecular weight Mn is determined by gel permeation chromatography using standard polystyrene as described in the description, and the insulating film has a film thickness t1 of 10 μm or more at a center portion of the long side of the rectangular cross-section, and the insulating film has a film thickness ratio t1/t2 of 0.98 to 1.35, and wherein the film thickness ratio t1/t2 is a ratio of the film thickness t1 at the center portion of the long side to a film thickness t2 at an edge portion of the long side of the rectangular cross-section, wherein the film thickness t1 at the center portion of the long side is an average value of two locations at an upper side and a lower side in the center portion of the long side, the film thickness t2 is an average value of four locations at upper sides and lower sides in both edge portions of the long side, and the film thickness t2 at the edge portion of the long side refers to the thickest part where roundness disappears in the edge portion of the insulating film and the long side of the flat conductive wire and a surface of the insulating film begin to be parallel to each other.