Provided is a transmission line transformer having increased signal efficiency. The transmission line transformer is formed on an integrated circuit (IC), wherein a first transmission line disposed in one direction. Second and third transmission lines have same length direction as the first transmission line and are spaced apart from each other in a lateral direction above or below the first transmission line. Accordingly, an area of the first transmission line and areas of the second and third transmission lines, which face each other, are increased, thereby improving a coupling factor. Also, since a secondary transmission line is divided into two regions and uses the second and third transmission lines that have narrower widths than the first transmission line, parasitic capacitance components generated between the first through third transmission lines and a semiconductor substrate may be decreased.