An annular core includes an upper core and a lower core. A coil is attached to the leg of the annular core in a way that the winding axis is aligned in the vertical direction. The surface of the upper core is covered by an upper cover formed of resin. The surface of the lower core is covered by the lower cover formed of resin. A casing formed of metal includes a bottom plate having an opening, and a side wall integrated with the bottom plate, and the lower core, the coil, and the upper core are housed in the casing. A part of the lower cover is exposed via the opening of the casing. A filler resin is filled in a gap between the circumference of the annular core and the coil, and the side wall of the casing or the lower cover.