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.