There are provided a waveguide forming apparatus, a dielectric waveguide forming apparatus, a pin structure and a high frequency circuit that can optimize a circuit portion provided therein and have high versatility. A waveguide is formed by allowing first and second conductive layers (6, 7) to cooperate with a plurality of control pins (2). A variable high frequency circuit forming portion is freely and simply changed by displacing each control pin (2) between a down-status indicated by Z1 and an up-status indicated by Z2.