To provide a high frequency line-waveguide converter in which conversion efficiency is high, and variations in conversion characteristics are small.

Concave and convex faces 7a, 7b are formed on a dielectric layer 5 inside a lower surface conductor layer 3, namely, a lower surface 7 of a dielectric matching unit 5a. Thus, an electromagnetic field of a resonance mode generated in the dielectric matching unit 5a can be changed and a resonance frequency is shifted, a frequency band in which the high frequency signal is transformed to the waveguide 6 is widened, and variations in the transforming characteristics due to manufacturing deviation can be made small.