A wire bundle includes insulated wires. The insulated wires each includes a conductor core covered with an insulator and is quad-twisted to form the wire bundle. The wire bundle has an annular shape including an inner perimeter and an outer perimeter in a cross section perpendicular to an axis line of the wire bundle. A shape of the outer perimeter is a square or a quasi-square. The quasi-square is a shape formed by curving at least one side of a square to a radial inside direction of the annular shape in the cross section. The insulated wires each has, in the cross section, a shape connecting a plurality of vertexes including two adjacent vertexes of the square or the quasi-square and two vertexes present on the inner perimeter.