A variable coupled inductor includes a first core, two conducting wires, a second core and a magnetic structure. The first core includes two first protruding portions, a second protruding portion and two grooves, wherein the second protruding portion is located between the two first protruding portions and each of the grooves is located between one of the first protruding portions and the second protruding portion. Each of the conducting wires is disposed in one of the grooves. The second core is disposed on the first core. A first gap is formed between each of the first protruding portions and the second core and a second gap is formed between the second protruding portion and the second core. The magnetic structure is disposed between the second protruding portion and the second core and distributed symmetrically with respect to a centerline of the second protruding portion.