At least two or more flat rectangular wires having been fed separately or simultaneously (two or more are superimposed) are integrated by being pinched in a width direction and a thickness direction by at least two or more pairs of rollers and are rolled and formed simultaneously in a forming part to be formed into two or more flat rectangular electric wires. The two formed electric wires are stacked in layers in a wind-up part while being wound into a disk shape to provide a multi-stage coil. Two or more systems up to the forming part of the winding apparatus may be disposed in a planar layout. Each system may supply one flat rectangular electric wire separately, and the supplied electric wires may be stacked in layers in the wind-up part while being superimposed. The coil may be molded entirely.