There is provided a transformer capable of easily securing an insulation distance between a core and coils. The transformer includes: a bobbin including a pipe shaped body part having a through-hole formed therein and flange parts protruding outwardly from both ends of the body part; a plurality of coils wound on the body part of the bobbin; and a core inserted into the through-hole of the bobbin to form a magnetic circuit, wherein both an outer surface and an outer peripheral surface of the flange parts are disposed to be spaced apart from an inner peripheral surface of a core by a predetermined interval.