Disclosed herein is a choke coil including: a core composed of first and second legs, a first flat plate connecting an upper end portion of the first leg and that of the second leg, and a second flat plate connecting a lower end portion of the first leg and that of the second leg; a primary coil wound around the first leg; and a secondary coil wound around the second leg, wherein a width of at least any one of the first flat plate and the second flat plate is greater than widths of the first leg and the second leg.