There is provided a thin transformer capable of being 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 bobbin part including a plurality of bobbins, each including a pipe shaped body part having a though-hole formed in an inner portion thereof, a flange part vertically protruding outwardly from both ends of the body part, and external connection terminals protruding from one side of a lower flange part formed at a lower end of the body part; a core inserted into the through-hole of the bobbin to thereby form a magnetic path; and a coil part including coils each wound around the plurality of bobbins, wherein the bobbin part includes an inner bobbin and an outer bobbin, and 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 opposed to each other.