PURPOSE: A transformer is provided to secure an insulation property and minimize the size of the transformer by securing a distance between coils around the inner bobbin and the outer bobbin. CONSTITUTION: A bobbin unit(10) is comprised of a plurality of bobbins which include a tubular body unit and a flange unit. The bobbin unit includes an outer bobbin(30) and an inner bobbin(20) which is inserted into a penetration hole of the outer bobbin. A flange unit of the inner bobbin and a flange unit of the outer bobbin are arranged on the same plane. A core(40) is inserted into the penetration hole of the bobbin and forms a magnetic path. A coil unit(50) includes coils wound around the plurality of bobbins.
