A planar dielectric integrated circuit is provided such that energy conversion loss between a planar dielectric line and electronic components is small and that impedance matching between them can be easily obtained. A planar dielectric line is provided by causing two slots to oppose each other with a dielectric plate interposed in between, a slot line and line-conversion conductor patterns are provided in the end portions of the planar dielectric line, and an FET is disposed in such a manner as to be extended over the slot line.