PURPOSE: A transformer is provided to easily secure an insulation between an outer bobbin and an outer connection terminal by protruding an external connection terminal of an inner bobbin to the outside of an outer bobbin. CONSTITUTION: A bobbin unit(10) is comprised of an outer bobbin(30) and a plurality of inner bobbins(20). The inner bobbin includes a tubular body unit, a flange unit, and a terminal coupling unit. The terminal coupling unit of the inner bobbin is protruded in an outer direction. A core(40) is inserted into a penetration hole of the bobbin and forms a magnetic path. A coil unit(50) includes coils which are respectively wound around the plurality of bobbins.
