A transformer capable of security insulting reliability and a power module having the same are provided. The transformer includes: a winding unit having at least one winding space in which a plurality of coils are wound in a stacked manner on an outer circumferential surface of a cylindrical body portion; and a terminal fastening unit formed to extend from one end of the winding unit in an outer diameter direction and having a plurality of external connection terminals fastened to an end thereof, wherein a width of the winding space is less than 0.45 times that of a diameter of the body portion.