A planar circuit having a conductive film on either main surface of a substrate. The conductive film on one of the main surfaces is patterned with two-dimensionally and repeatedly arranged unit cells, which are basic conductor patterns. Each of the unit cells has a capacitive region at the center thereof. Capacitance is induced between the center area and the conductor film formed on the main surface of the substrate opposite the center area. An area located near the middle of each of sides in the peripheral portion serves as an inductive region. In any two adjacent unit cells, the inductive regions have a multiple spiral-shaped conductor pattern, in which the center ends thereof are connected to each other at a halfway position between the two unit cells, and the outer peripheral ends thereof are connected to the capacitive regions.