Disclosed herein is a common mode filter that comprises a drum core including a winding core portion and a pair of flange portions provided at both ends of the winding core portion, and first and second wires wound around the winding core portion so as to form a pair-wire for each turn. The first and second wires includes one or a plurality of sparsely-wound portions in which the first and second wires are wound with adjacent pair-wires spaced from each other, and one or a plurality of closely-wound portions in which the first and second wires are wound with adjacent pair-wires in close contact with each other.