PURPOSE: To obtain a triplate line circuit which can stably support triplate lines packaged in a casing and can be supported at an arbitrary position.

CONSTITUTION: Among a pair of downside and upside supporting bodies 4A and 4B for holding triplate lines 3 in the casing (case 1 and cover 2), one supporting body 4B is supported to the casing by a screw mechanism and the position for supporting the triplate lines 3 can be changed by this screw mechanism. Further, the other supporting body 4B is equipped with a screw mechanism to screw an adjusting screw 6 for adjusting the electric characteristics of the triplate lines 3, as well.