A flyback transformer includes a coil unit, a variable resistor unit detachably mounted on the coil unit and a connector for electrically connecting the coil unit and the variable resistor unit. The coil unit has a casing, primary and secondary coils accommodated in the casing, and a terminal which is electrically connected to a center tap of the secondary coil through a lead line extending inside the casing. The variable resistor unit has a circuit board deposited with ohmic resistance stripes and a terminal which is electrically connected to the circuit board. The connector having a U-shape configuration electrically connects the terminal of the coil unit and the terminal of the variable resistor unit.