Circuit substrate, filter circuit, and capacitance element

A circuit substrate includes a first electrode connecting a capacitance element, a first inductance element including a first interconnect that extends from one end connected to the first electrode to another end across a region at which the capacitance element is to be mounted, a second inductance element including a second interconnect that extends from one end connected to the first electrode to another end across the region at which the capacitance element is to be mounted from a side opposite to the first interconnect, an input terminal connected to the another end of the second interconnect, an output terminal connected to the another end of the first interconnect, and a second electrode that provides a capacitance between the output terminal and the second electrode, wherein the capacitance provided by the output terminal and the second electrode is equal to or larger than a capacitance of the capacitance element.