A transmission line driver circuit includes: a transmission line driving amplifier having a first transmission terminal and a second transmission terminal; a first signal node; a second signal node; a first adjustable resistor positioned between the first transmission terminal and the first signal node; a second adjustable resistor positioned between the second transmission terminal and the second signal node; an internal node; a first divider resistor positioned between the first signal node and the internal node; a second divider resistor positioned between the second signal node and the internal node; a comparing circuit for comparing a divided voltage at the internal node with a reference voltage to generate a comparison signal; and an adjusting circuit for adjusting resistance of at least one of the first and second adjustable resistors according to the comparison signal.