A thin transformer to be used in a thin display device such as a liquid crystal display (LCD) device and a light emitting diode (LED) display device. The transformer includes a plurality of bobbins, each including a pipe shaped body having a though-hole formed in an inner portion thereof, a flange vertically protruding outwardly from both ends of the body, and external connection terminals protruding from one side of a lower flange formed at a lower end of the body; a core inserted into through-holes of the bobbins to form a magnetic path; and coils each wound around the plurality of bobbins. The bobbins include inner and outer bobbins. The inner bobbin is coupled to the outer bobbin such that the external connection terminals of the inner bobbin and the external connection terminals of the outer bobbin are mutually opposed.