A coil apparatus comprising: a core having a main body and a segment that are obtained by a molded core including an annular magnetic body made of a magnetic material and a resin covering part that covers the magnetic body being cut at a first cutting part and a second cutting part that transect an outer peripheral surface and an inner peripheral surface and approach each other toward the inner peripheral surface of the molded core , the main body having a main body-side first end face formed by the cutting at the first cutting part and a main body-side second end face formed by the cutting at the second cutting part , and the segment having a segment-side first end face formed by the cutting at the first cutting part and a segment-side second end face formed by the cutting at the second cutting part , wherein the segment is disposed in a cutout part formed between the main body-side first end face and the main body-side second end face of the main body such that the main body-side first end face and the segment-side first end face and the main body-side second end face and the segment-side second end face are placed against each other, respectively, and wherein the resin covering part has a main body-side flange part that projects toward the outer peripheral side and/or the lateral side from an end edge on the main body-side second end face side, and a segment-side flange part that projects toward the outer peripheral side and/or the lateral side from an end face on the segment-side second end face side; a coil wound around the core ; and a casing mounted with the core , the casing having a recess into which the main body-side flange part and the segment-side flange part are inserted. a core having a main body and a segment that are obtained by a molded core including an annular magnetic body made of a magnetic material and a resin covering part that covers the magnetic body being cut at a first cutting part and a second cutting part that transect an outer peripheral surface and an inner peripheral surface and approach each other toward the inner peripheral surface of the molded core , the main body having a main body-side first end face formed by the cutting at the first cutting part and a main body-side second end face formed by the cutting at the second cutting part , and the segment having a segment-side first end face formed by the cutting at the first cutting part and a segment-side second end face formed by the cutting at the second cutting part , wherein the segment is disposed in a cutout part formed between the main body-side first end face and the main body-side second end face of the main body such that the main body-side first end face and the segment-side first end face and the main body-side second end face and the segment-side second end face are placed against each other, respectively, and wherein the resin covering part has a main body-side flange part that projects toward the outer peripheral side and/or the lateral side from an end edge on the main body-side second end face side, and a segment-side flange part that projects toward the outer peripheral side and/or the lateral side from an end face on the segment-side second end face side; a coil wound around the core ; and a casing mounted with the core , the casing having a recess into which the main body-side flange part and the segment-side flange part are inserted. <EOS>