In a high frequency signal line, a first signal line extends along a first dielectric element assembly, a first reference ground conductor extends along the first signal line, a second signal line is provided in or on the second dielectric element assembly and extends along the second dielectric element assembly, a second reference ground conductor is provided in or on the second dielectric element assembly and extends along the second signal line. A portion of a bottom surface at an end of the first dielectric element assembly and a portion of the top surface at an end of the second dielectric element assembly are joined together such that a joint portion of the first and second dielectric element assemblies includes a corner. The second signal line and the first signal line are electrically coupled together. The first and second reference ground conductors are electrically coupled together.