A method of manufacturing a concentrated winding coil comprising a helical structure and having a predetermined length along a helical loop of the helical structure, the method comprising: providing a plurality of flat conductors, wherein each of the flat conductors has a first end and a second end that are flat and are terminal portions of a flat conductor with respect to a direction of the helical loop, and when the plurality of flat conductors is arranged to form a structure having the helical structure by connecting flat conductors at the first and second ends thereof, the structure has a length along the helical loop of the helical structure that is longer than the predetermined length of the coil along the helical loop; pressing the first end of one of the plurality of flat conductors against the second end of another of the plurality of flat conductors in the direction of the helical loop so that the two flat conductors are cold-welded and a total length of the two welded flat conductors along the helical loop is shortened by the pressing; and repeating the pressing for all of the plurality of flat conductors so that a total length of the plurality of welded flat conductors along the helical loop becomes equal to the predetermined length of the coil along the helical loop, wherein the welding is performed by utilizing a linear portion of each of the flat conductors, wherein a region of one turn of the helical structure has a first linear part extending along a first direction, a second linear part extending along a second direction, and a corner portion connecting the first linear part and the second linear part therebetween, wherein the welded portion of the flat conductors is formed at an area excluding the corner portion. providing a plurality of flat conductors, wherein each of the flat conductors has a first end and a second end that are flat and are terminal portions of a flat conductor with respect to a direction of the helical loop, and when the plurality of flat conductors is arranged to form a structure having the helical structure by connecting flat conductors at the first and second ends thereof, the structure has a length along the helical loop of the helical structure that is longer than the predetermined length of the coil along the helical loop; pressing the first end of one of the plurality of flat conductors against the second end of another of the plurality of flat conductors in the direction of the helical loop so that the two flat conductors are cold-welded and a total length of the two welded flat conductors along the helical loop is shortened by the pressing; and repeating the pressing for all of the plurality of flat conductors so that a total length of the plurality of welded flat conductors along the helical loop becomes equal to the predetermined length of the coil along the helical loop, wherein the welding is performed by utilizing a linear portion of each of the flat conductors, wherein a region of one turn of the helical structure has a first linear part extending along a first direction, a second linear part extending along a second direction, and a corner portion connecting the first linear part and the second linear part therebetween, wherein the welded portion of the flat conductors is formed at an area excluding the corner portion.