In order to provide a transformer and an electric power converter which are less likely to become deteriorated with time and which have stable insulation performance, the transformer according to the present invention is provided with: a core; a bobbin in which a low-voltage-side primary winding and a high-voltage-side secondary winding are disposed along the central magnetic leg of the core; and a bobbin support part that supports the bobbin at an end of the bobbin on the primary winding side, such that an air gap is provided between the central magnetic leg of the core and a surface of the bobbin corresponding to the secondary winding.