When joining end faces of a plurality of soft magnetic sheets which are superposed in the sheet thickness direction and which are bent at parts forming corner areas of a core, offset of positions of the end faces from the desired positions is suppressed.
In a region of a window part comprised of a region inside of a first part 110 and second part 120, a third part 130 with a length in a longitudinal direction (X-axial direction) the same as a length in the X-axial direction of the window part at the position where the third part 130 is arranged is arranged so as to contact the region of the inner circumferential surface between the first corner area 101 and third corner area 103.