A field element core has field magnet through holes and connecting portions. The field magnet through holes are circumferentially arranged in a circumferential direction around a given direction, and are adjacent each other in the circumferential direction to form pairs. Seen from the given direction, field magnet through holes forming the same pair both extend along a certain one direction determined for each pair. A connecting portion is provided between the field magnet through holes of the same pair, and has the ends as its sides. The sides of the connecting portion are curved in a concave shape as a whole. Specifically, seen from the given direction, a tangent to the side is along the direction of extension of the connecting portion only at a certain one position between both ends of the side. The same holds true for the side.