A circular wire with a circular cross section is wound on a coil reel. When a winding-form motor rotates a winding form, the circular wire is pulled and drawn from the coil reel. Rectangular forming rollers press the circular wire, so that a rectangular wire with a rectangular cross section is formed. The rectangular wire is directly wound on the winding form to be formed into a rectangular-wire coil. Because forming rectangular wire and winding on the winding form are carried out in a sequence of contiguous processes, a separate process for removing torsion set of the rectangular wire is unnecessary. The rectangular-wire coil can be formed from inexpensive circular material wire by a simple and low-cost apparatus. It is also possible and preferable to make dimensions and a shape of the rectangular wire variable by controlling clearance widths between the forming rollers and tension acting on the rectangular wire that has passed through the rollers.