Provided is a transmission line transformer, and more particularly, a transmission line transformer capable of decreasing a power loss caused by a parasitic resistance component of the transmission line transformer and improving a coupling factor by forming a primary transmission line and a secondary transmission line parallel to each other on an integrated circuit (IC) by using a highest layer metal line, and forming a lower layer metal line immediately below the highest layer metal line in addition to the highest layer metal line in a region where the primary transmission line and the secondary transmission line face each other, while forming the transmission line transformer used in a high frequency circuit via a semiconductor process.