A transformer comprises a circuit board, an iron core, a winding set and a plurality of magnetic conduction elements. The circuit board has a plurality of electric conduction holes connected via at least one power connection wire. The iron core is located on the circuit board and has a first winding section and a second winding section. The winding set is wound on the first winding section. Each magnetic conduction element has a connecting section located on the iron core and an input section and an output section inserted into the electric conduction holes. The output section of one magnetic conduction element is connected to the input section of another magnetic conduction element through the power connection wire, thereby the magnetic conduction elements and power connection wire form a magnetic conduction winding set which generates magnetic coupling with the winding set through the iron core.