There is provided a transformer having a minimized leakage inductance. The transformer includes: a winding part including a pipe shaped body part having a plurality of coils wound therearound and flange parts extended from both ends of the body part in an outer diameter direction thereof; and a core coupled to the winding part, wherein a flange part formed at one end of the body part includes at least one lead groove, and the coils are led to the outside of the winding part through the at least one lead groove.