There are provided a thin transformer capable of being used in a thin display device such as a liquid crystal display (LCD) device, a light emitting diode (LED) display device, and a flat panel display device including the same. The transformer includes: a bobbin part including inner and outer bobbins each including a pipe shaped body part having a though-hole formed in an inner portion thereof and a flange part protruding outwardly from both ends of the body part; coils respectively wound around the inner and outer bobbins; and a core electromagnetically coupled to the coils to thereby form a magnetic path, wherein the inner bobbin is inserted into the through-hole of the outer bobbin to thereby be coupled to the outer bobbin and at least one of the inner and outer bobbins includes the flange part having a width larger than a thickness of the body part.