A transformer for cathode tube inverter. The transformer includes an iron core assembly having first, second, third and fourth iron cores, each having a U-shape, and a first wire rack having a first wire winding portion, and a first hollow portion for accommodating the first iron. The transformer further includes a second wire rack having a hollow second wire winding portion, and a second portion for accommodating the second iron core and the third iron core, a third wire rack having a third wire winding portion, and a third hollow wire portion for accommodating the fourth iron core and a primary coil is shared within the iron cores. The primary coil and secondary coils are completely isolated with respect to electric circuits, and the secondary coils are completely or mostly, as well as mutually isolated with respect to magnetic circuits.