A winding method of forming a coil by edgewise bending a flat rectangular conductor comprises a step of edgewise bending the rectangular conductor to form edgewise bending portions so that two predetermined two adjacent bent portions are formed so that an outward bulging portion to be generated by edgewise-bending of the flat rectangular conductor is generated in a concentrated manner in a side between the two edgewise bent portions, and the side having the bulging portion constitutes each of a pair of opposite sides of the coil.